diff --git a/core/common/src/DateTimePeriod.kt b/core/common/src/DateTimePeriod.kt
index f9b2d3f3..5b5141d5 100644
--- a/core/common/src/DateTimePeriod.kt
+++ b/core/common/src/DateTimePeriod.kt
@@ -9,7 +9,9 @@ import kotlinx.datetime.internal.*
 import kotlinx.datetime.serializers.DatePeriodIso8601Serializer
 import kotlinx.datetime.serializers.DateTimePeriodIso8601Serializer
 import kotlinx.datetime.serializers.DatePeriodComponentSerializer
+import kotlinx.datetime.serializers.DatePeriodSerializer
 import kotlinx.datetime.serializers.DateTimePeriodComponentSerializer
+import kotlinx.datetime.serializers.DateTimePeriodSerializer
 import kotlin.math.*
 import kotlin.time.Duration
 import kotlinx.serialization.Serializable
@@ -63,13 +65,14 @@ import kotlinx.serialization.Serializable
  * `DateTimePeriod` can also be returned as the result of instant arithmetic operations (see [Instant.periodUntil]).
  *
  * Additionally, there are several `kotlinx-serialization` serializers for [DateTimePeriod]:
- * - [DateTimePeriodIso8601Serializer] for the ISO 8601 format;
+ * - The default serializer, delegating to [toString] and [parse].
+ * - [DateTimePeriodIso8601Serializer] for the ISO 8601 format.
  * - [DateTimePeriodComponentSerializer]  for an object with components.
  *
  * @sample kotlinx.datetime.test.samples.DateTimePeriodSamples.construction
  * @sample kotlinx.datetime.test.samples.DateTimePeriodSamples.simpleParsingAndFormatting
  */
-@Serializable(with = DateTimePeriodIso8601Serializer::class)
+@Serializable(with = DateTimePeriodSerializer::class)
 // TODO: could be error-prone without explicitly named params
 public sealed class DateTimePeriod {
     internal abstract val totalMonths: Int
@@ -426,7 +429,7 @@ public fun String.toDateTimePeriod(): DateTimePeriod = DateTimePeriod.parse(this
  *
  * @sample kotlinx.datetime.test.samples.DatePeriodSamples.simpleParsingAndFormatting
  */
-@Serializable(with = DatePeriodIso8601Serializer::class)
+@Serializable(with = DatePeriodSerializer::class)
 public class DatePeriod internal constructor(
     internal override val totalMonths: Int,
     override val days: Int,
diff --git a/core/common/src/Instant.kt b/core/common/src/Instant.kt
index 36fd40d2..7437bd1c 100644
--- a/core/common/src/Instant.kt
+++ b/core/common/src/Instant.kt
@@ -7,8 +7,7 @@ package kotlinx.datetime
 
 import kotlinx.datetime.format.*
 import kotlinx.datetime.internal.*
-import kotlinx.datetime.serializers.InstantIso8601Serializer
-import kotlinx.datetime.serializers.InstantComponentSerializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 import kotlin.time.*
 
@@ -189,12 +188,13 @@ import kotlin.time.*
  * ```
  *
  * Additionally, there are several `kotlinx-serialization` serializers for [Instant]:
+ * - The default serializer, delegating to [toString] and [parse].
  * - [InstantIso8601Serializer] for the ISO 8601 extended format.
  * - [InstantComponentSerializer] for an object with components.
  *
  * @see LocalDateTime for a user-visible representation of moments in time in an unspecified time zone.
  */
-@Serializable(with = InstantIso8601Serializer::class)
+@Serializable(with = InstantSerializer::class)
 public expect class Instant : Comparable<Instant> {
 
     /**
diff --git a/core/common/src/LocalDate.kt b/core/common/src/LocalDate.kt
index 0146d6f9..eb80dc01 100644
--- a/core/common/src/LocalDate.kt
+++ b/core/common/src/LocalDate.kt
@@ -56,6 +56,7 @@ import kotlinx.serialization.Serializable
  * See sample 4.
  *
  * Additionally, there are several `kotlinx-serialization` serializers for [LocalDate]:
+ * - The default serializer, delegating to [toString] and [parse].
  * - [LocalDateIso8601Serializer] for the ISO 8601 extended format.
  * - [LocalDateComponentSerializer] for an object with components.
  *
@@ -64,7 +65,7 @@ import kotlinx.serialization.Serializable
  * @sample kotlinx.datetime.test.samples.LocalDateSamples.simpleParsingAndFormatting
  * @sample kotlinx.datetime.test.samples.LocalDateSamples.customFormat
  */
-@Serializable(with = LocalDateIso8601Serializer::class)
+@Serializable(with = LocalDateSerializer::class)
 public expect class LocalDate : Comparable<LocalDate> {
     public companion object {
         /**
diff --git a/core/common/src/LocalDateTime.kt b/core/common/src/LocalDateTime.kt
index db4533b8..09691d3b 100644
--- a/core/common/src/LocalDateTime.kt
+++ b/core/common/src/LocalDateTime.kt
@@ -6,8 +6,7 @@
 package kotlinx.datetime
 
 import kotlinx.datetime.format.*
-import kotlinx.datetime.serializers.LocalDateTimeIso8601Serializer
-import kotlinx.datetime.serializers.LocalDateTimeComponentSerializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 
 /**
@@ -94,6 +93,7 @@ import kotlinx.serialization.Serializable
  * See sample 4.
  *
  * Additionally, there are several `kotlinx-serialization` serializers for [LocalDateTime]:
+ * - The default serializer, delegating to [toString] and [parse].
  * - [LocalDateTimeIso8601Serializer] for the ISO 8601 extended format.
  * - [LocalDateTimeComponentSerializer] for an object with components.
  *
@@ -105,7 +105,7 @@ import kotlinx.serialization.Serializable
  * @sample kotlinx.datetime.test.samples.LocalDateTimeSamples.simpleParsingAndFormatting
  * @sample kotlinx.datetime.test.samples.LocalDateTimeSamples.customFormat
  */
-@Serializable(with = LocalDateTimeIso8601Serializer::class)
+@Serializable(with = LocalDateTimeSerializer::class)
 public expect class LocalDateTime : Comparable<LocalDateTime> {
     public companion object {
 
diff --git a/core/common/src/LocalTime.kt b/core/common/src/LocalTime.kt
index 695a1090..f27d6401 100644
--- a/core/common/src/LocalTime.kt
+++ b/core/common/src/LocalTime.kt
@@ -7,8 +7,7 @@ package kotlinx.datetime
 
 import kotlinx.datetime.LocalDate.Companion.parse
 import kotlinx.datetime.format.*
-import kotlinx.datetime.serializers.LocalTimeIso8601Serializer
-import kotlinx.datetime.serializers.LocalTimeComponentSerializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 
 
@@ -68,6 +67,7 @@ import kotlinx.serialization.Serializable
  * See sample 4.
  *
  * Additionally, there are several `kotlinx-serialization` serializers for [LocalTime]:
+ * - The default serializer, delegating to [toString] and [parse].
  * - [LocalTimeIso8601Serializer] for the ISO 8601 extended format,
  * - [LocalTimeComponentSerializer] for an object with components.
  *
@@ -76,7 +76,7 @@ import kotlinx.serialization.Serializable
  * @sample kotlinx.datetime.test.samples.LocalTimeSamples.simpleParsingAndFormatting
  * @sample kotlinx.datetime.test.samples.LocalTimeSamples.customFormat
  */
-@Serializable(LocalTimeIso8601Serializer::class)
+@Serializable(LocalTimeSerializer::class)
 public expect class LocalTime : Comparable<LocalTime> {
     public companion object {
 
diff --git a/core/common/src/UtcOffset.kt b/core/common/src/UtcOffset.kt
index 97c5e410..8a5cc769 100644
--- a/core/common/src/UtcOffset.kt
+++ b/core/common/src/UtcOffset.kt
@@ -6,7 +6,7 @@
 package kotlinx.datetime
 
 import kotlinx.datetime.format.*
-import kotlinx.datetime.serializers.UtcOffsetSerializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 
 /**
@@ -47,12 +47,14 @@ import kotlinx.serialization.Serializable
  * [parse] and [UtcOffset.format] both support custom formats created with [Format] or defined in [Formats].
  * See sample 3.
  *
- * To serialize and deserialize [UtcOffset] values with `kotlinx-serialization`, use the [UtcOffsetSerializer].
+ * To serialize and deserialize [UtcOffset] values with `kotlinx-serialization`, use the default serializer,
+ * or [UtcOffsetIso8601Serializer] for the ISO 8601 format explicitly.
  *
  * @sample kotlinx.datetime.test.samples.UtcOffsetSamples.construction
  * @sample kotlinx.datetime.test.samples.UtcOffsetSamples.simpleParsingAndFormatting
  * @sample kotlinx.datetime.test.samples.UtcOffsetSamples.customFormat
  */
+@Suppress("DEPRECATION")
 @Serializable(with = UtcOffsetSerializer::class)
 public expect class UtcOffset {
     /**
diff --git a/core/common/src/serializers/DateTimePeriodSerializers.kt b/core/common/src/serializers/DateTimePeriodSerializers.kt
index e5d904fc..ac76db34 100644
--- a/core/common/src/serializers/DateTimePeriodSerializers.kt
+++ b/core/common/src/serializers/DateTimePeriodSerializers.kt
@@ -19,7 +19,7 @@ import kotlinx.serialization.encoding.*
 public object DateTimePeriodComponentSerializer: KSerializer<DateTimePeriod> {
 
     override val descriptor: SerialDescriptor =
-        buildClassSerialDescriptor("kotlinx.datetime.DateTimePeriod") {
+        buildClassSerialDescriptor("kotlinx.datetime.DateTimePeriod components") {
             element<Int>("years", isOptional = true)
             element<Int>("months", isOptional = true)
             element<Int>("days", isOptional = true)
@@ -81,7 +81,7 @@ public object DateTimePeriodComponentSerializer: KSerializer<DateTimePeriod> {
 public object DateTimePeriodIso8601Serializer: KSerializer<DateTimePeriod> {
 
     override val descriptor: SerialDescriptor =
-        PrimitiveSerialDescriptor("kotlinx.datetime.DateTimePeriod", PrimitiveKind.STRING)
+        PrimitiveSerialDescriptor("kotlinx.datetime.DateTimePeriod ISO", PrimitiveKind.STRING)
 
     override fun deserialize(decoder: Decoder): DateTimePeriod =
         DateTimePeriod.parse(decoder.decodeString())
@@ -110,7 +110,7 @@ public object DatePeriodComponentSerializer: KSerializer<DatePeriod> {
     private fun unexpectedNonzero(fieldName: String, value: Int) = unexpectedNonzero(fieldName, value.toLong())
 
     override val descriptor: SerialDescriptor =
-        buildClassSerialDescriptor("kotlinx.datetime.DatePeriod") {
+        buildClassSerialDescriptor("kotlinx.datetime.DatePeriod components") {
             element<Int>("years", isOptional = true)
             element<Int>("months", isOptional = true)
             element<Int>("days", isOptional = true)
@@ -166,7 +166,7 @@ public object DatePeriodComponentSerializer: KSerializer<DatePeriod> {
 public object DatePeriodIso8601Serializer: KSerializer<DatePeriod> {
 
     override val descriptor: SerialDescriptor =
-        PrimitiveSerialDescriptor("kotlinx.datetime.DatePeriod", PrimitiveKind.STRING)
+        PrimitiveSerialDescriptor("kotlinx.datetime.DatePeriod ISO", PrimitiveKind.STRING)
 
     override fun deserialize(decoder: Decoder): DatePeriod =
         when (val period = DateTimePeriod.parse(decoder.decodeString())) {
@@ -179,3 +179,15 @@ public object DatePeriodIso8601Serializer: KSerializer<DatePeriod> {
     }
 
 }
+
+@PublishedApi
+internal object DateTimePeriodSerializer: KSerializer<DateTimePeriod> by DateTimePeriodIso8601Serializer {
+    override val descriptor =
+        PrimitiveSerialDescriptor("kotlinx.datetime.DateTimePeriod", PrimitiveKind.STRING)
+}
+
+@PublishedApi
+internal object DatePeriodSerializer: KSerializer<DatePeriod> by DatePeriodIso8601Serializer {
+    override val descriptor =
+        PrimitiveSerialDescriptor("kotlinx.datetime.DatePeriod", PrimitiveKind.STRING)
+}
diff --git a/core/common/src/serializers/InstantSerializers.kt b/core/common/src/serializers/InstantSerializers.kt
index c64bdf47..1b3ccdd9 100644
--- a/core/common/src/serializers/InstantSerializers.kt
+++ b/core/common/src/serializers/InstantSerializers.kt
@@ -5,7 +5,9 @@
 
 package kotlinx.datetime.serializers
 
-import kotlinx.datetime.Instant
+import kotlinx.datetime.*
+import kotlinx.datetime.format.DateTimeComponents
+import kotlinx.datetime.format.DateTimeFormat
 import kotlinx.serialization.*
 import kotlinx.serialization.descriptors.*
 import kotlinx.serialization.encoding.*
@@ -15,19 +17,18 @@ import kotlinx.serialization.encoding.*
  *
  * JSON example: `"2020-12-09T09:16:56.000124Z"`
  *
- * @see Instant.toString
- * @see Instant.parse
+ * @see DateTimeComponents.Formats.ISO_DATE_TIME_OFFSET
  */
 public object InstantIso8601Serializer : KSerializer<Instant> {
 
     override val descriptor: SerialDescriptor =
-        PrimitiveSerialDescriptor("kotlinx.datetime.Instant", PrimitiveKind.STRING)
+        PrimitiveSerialDescriptor("kotlinx.datetime.Instant ISO", PrimitiveKind.STRING)
 
     override fun deserialize(decoder: Decoder): Instant =
-        Instant.parse(decoder.decodeString())
+        Instant.parse(decoder.decodeString(), DateTimeComponents.Formats.ISO_DATE_TIME_OFFSET)
 
     override fun serialize(encoder: Encoder, value: Instant) {
-        encoder.encodeString(value.toString())
+        encoder.encodeString(value.format(DateTimeComponents.Formats.ISO_DATE_TIME_OFFSET))
     }
 
 }
@@ -40,7 +41,7 @@ public object InstantIso8601Serializer : KSerializer<Instant> {
 public object InstantComponentSerializer : KSerializer<Instant> {
 
     override val descriptor: SerialDescriptor =
-        buildClassSerialDescriptor("kotlinx.datetime.Instant") {
+        buildClassSerialDescriptor("kotlinx.datetime.Instant components") {
             element<Long>("epochSeconds")
             element<Long>("nanosecondsOfSecond", isOptional = true)
         }
@@ -75,3 +76,70 @@ public object InstantComponentSerializer : KSerializer<Instant> {
     }
 
 }
+
+/**
+ * An abstract serializer for [Instant] values that uses
+ * a custom [DateTimeFormat] for serializing to and deserializing.
+ *
+ * [format] should be a format that includes enough components to unambiguously define a date, a time, and a UTC offset.
+ * See [Instant.parse] for details of how deserialization is performed.
+ *
+ * [name] is the name of the serializer.
+ * The [SerialDescriptor.serialName] of the resulting serializer is `kotlinx.datetime.Instant serializer `[name].
+ * [SerialDescriptor.serialName] must be unique across all serializers in the same serialization context.
+ * When defining a serializer in a library, it is recommended to use the fully qualified class name in [name]
+ * to avoid conflicts with serializers defined by other libraries and client code.
+ *
+ * When serializing, the [Instant] value is formatted as a string using the specified [format]
+ * in the [ZERO][UtcOffset.ZERO] UTC offset.
+ *
+ * This serializer is abstract and must be subclassed to provide a concrete serializer.
+ * Example:
+ * ```
+ * // serializes LocalDateTime(2008, 6, 30, 11, 5, 30).toInstant(TimeZone.UTC)
+ * // as the string "Mon, 30 Jun 2008 11:05:30 GMT"
+ * object Rfc1123InstantSerializer : FormattedInstantSerializer(
+ *     "my.package.RFC1123", DateTimeComponents.Formats.RFC_1123
+ * )
+ * ```
+ *
+ * Note that [Instant] is [kotlinx.serialization.Serializable] by default,
+ * so it is not necessary to create custom serializers when the format is not important.
+ * Additionally, [InstantIso8601Serializer] is provided for the ISO 8601 format.
+ */
+public abstract class FormattedInstantSerializer(
+    name: String,
+    private val format: DateTimeFormat<DateTimeComponents>,
+) : KSerializer<Instant> {
+    override val descriptor: SerialDescriptor =
+        PrimitiveSerialDescriptor("kotlinx.datetime.Instant serializer $name", PrimitiveKind.STRING)
+
+    override fun deserialize(decoder: Decoder): Instant =
+        Instant.parse(decoder.decodeString(), format)
+
+    override fun serialize(encoder: Encoder, value: Instant) {
+        encoder.encodeString(value.format(format))
+    }
+
+    @OptIn(ExperimentalSerializationApi::class)
+    override fun toString(): String = descriptor.serialName
+}
+
+/**
+ * A serializer for [Instant] that uses the default [Instant.toString]/[Instant.parse].
+ *
+ * JSON example: `"2020-12-09T09:16:56.000124Z"`
+ */
+@PublishedApi internal object InstantSerializer : KSerializer<Instant> {
+
+    override val descriptor: SerialDescriptor =
+        PrimitiveSerialDescriptor("kotlinx.datetime.Instant", PrimitiveKind.STRING)
+
+    override fun deserialize(decoder: Decoder): Instant =
+        Instant.parse(decoder.decodeString())
+
+    override fun serialize(encoder: Encoder, value: Instant) {
+        encoder.encodeString(value.toString())
+    }
+
+}
diff --git a/core/common/src/serializers/LocalDateSerializers.kt b/core/common/src/serializers/LocalDateSerializers.kt
index e1c1c5e9..b684b44f 100644
--- a/core/common/src/serializers/LocalDateSerializers.kt
+++ b/core/common/src/serializers/LocalDateSerializers.kt
@@ -6,6 +6,7 @@
 package kotlinx.datetime.serializers
 
 import kotlinx.datetime.LocalDate
+import kotlinx.datetime.format.DateTimeFormat
 import kotlinx.serialization.*
 import kotlinx.serialization.descriptors.*
 import kotlinx.serialization.encoding.*
@@ -15,22 +16,10 @@ import kotlinx.serialization.encoding.*
  *
  * JSON example: `"2020-01-01"`
  *
- * @see LocalDate.parse
- * @see LocalDate.toString
+ * @see LocalDate.Formats.ISO
  */
-public object LocalDateIso8601Serializer: KSerializer<LocalDate> {
-
-    override val descriptor: SerialDescriptor =
-        PrimitiveSerialDescriptor("kotlinx.datetime.LocalDate", PrimitiveKind.STRING)
-
-    override fun deserialize(decoder: Decoder): LocalDate =
-        LocalDate.parse(decoder.decodeString())
-
-    override fun serialize(encoder: Encoder, value: LocalDate) {
-        encoder.encodeString(value.toString())
-    }
-
-}
+public object LocalDateIso8601Serializer : KSerializer<LocalDate>
+by LocalDate.Formats.ISO.asKSerializer("kotlinx.datetime.LocalDate ISO")
 
 /**
  * A serializer for [LocalDate] that represents a value as its components.
@@ -40,7 +29,7 @@ public object LocalDateIso8601Serializer: KSerializer<LocalDate> {
 public object LocalDateComponentSerializer: KSerializer<LocalDate> {
 
     override val descriptor: SerialDescriptor =
-        buildClassSerialDescriptor("kotlinx.datetime.LocalDate") {
+        buildClassSerialDescriptor("kotlinx.datetime.LocalDate components") {
             element<Int>("year")
             element<Short>("month")
             element<Short>("day")
@@ -76,3 +65,63 @@ public object LocalDateComponentSerializer: KSerializer<LocalDate> {
     }
 
 }
+
+/**
+ * An abstract serializer for [LocalDate] values that uses
+ * a custom [DateTimeFormat] to serialize and deserialize the value.
+ *
+ * [name] is the name of the serializer.
+ * The [SerialDescriptor.serialName] of the resulting serializer is `kotlinx.datetime.LocalDate serializer `[name].
+ * [SerialDescriptor.serialName] must be unique across all serializers in the same serialization context.
+ * When defining a serializer in a library, it is recommended to use the fully qualified class name in [name]
+ * to avoid conflicts with serializers defined by other libraries and client code.
+ *
+ * This serializer is abstract and must be subclassed to provide a concrete serializer.
+ * Example:
+ * ```
+ * // serializes LocalDate(2020, 1, 4) as the string "20200104"
+ * object IsoBasicLocalDateSerializer :
+ *     FormattedLocalDateSerializer("my.package.ISO_BASIC", LocalDate.Formats.ISO_BASIC)
+ * ```
+ *
+ * Note that [LocalDate] is [kotlinx.serialization.Serializable] by default,
+ * so it is not necessary to create custom serializers when the format is not important.
+ * Additionally, [LocalDateIso8601Serializer] is provided for the ISO 8601 format.
+ */
+public abstract class FormattedLocalDateSerializer(
+    name: String, format: DateTimeFormat<LocalDate>
+) : KSerializer<LocalDate> by format.asKSerializer("kotlinx.datetime.LocalDate serializer $name")
+
+internal fun <T> DateTimeFormat<T>.asKSerializer(serialName: String): KSerializer<T> =
+    object : KSerializer<T> {
+        override val descriptor: SerialDescriptor =
+            PrimitiveSerialDescriptor(serialName, PrimitiveKind.STRING)
+
+        override fun deserialize(decoder: Decoder): T = parse(decoder.decodeString())
+
+        override fun serialize(encoder: Encoder, value: T) {
+            encoder.encodeString(format(value))
+        }
+
+        override fun toString(): String = serialName
+    }
+
+/**
+ * A serializer for [LocalDate] that uses the default [LocalDate.toString]/[LocalDate.parse].
+ *
+ * JSON example: `"2020-01-01"`
+ */
+@PublishedApi
+internal object LocalDateSerializer: KSerializer<LocalDate> {
+
+    override val descriptor: SerialDescriptor =
+        PrimitiveSerialDescriptor("kotlinx.datetime.LocalDate", PrimitiveKind.STRING)
+
+    override fun deserialize(decoder: Decoder): LocalDate =
+        LocalDate.parse(decoder.decodeString())
+
+    override fun serialize(encoder: Encoder, value: LocalDate) {
+        encoder.encodeString(value.toString())
+    }
+
+}
diff --git a/core/common/src/serializers/LocalDateTimeSerializers.kt b/core/common/src/serializers/LocalDateTimeSerializers.kt
index 73f29115..40f60742 100644
--- a/core/common/src/serializers/LocalDateTimeSerializers.kt
+++ b/core/common/src/serializers/LocalDateTimeSerializers.kt
@@ -6,6 +6,7 @@
 package kotlinx.datetime.serializers
 
 import kotlinx.datetime.*
+import kotlinx.datetime.format.DateTimeFormat
 import kotlinx.serialization.*
 import kotlinx.serialization.descriptors.*
 import kotlinx.serialization.encoding.*
@@ -15,22 +16,10 @@ import kotlinx.serialization.encoding.*
  *
  * JSON example: `"2007-12-31T23:59:01"`
  *
- * @see LocalDateTime.parse
- * @see LocalDateTime.toString
+ * @see LocalDateTime.Formats.ISO
  */
-public object LocalDateTimeIso8601Serializer: KSerializer<LocalDateTime> {
-
-    override val descriptor: SerialDescriptor =
-        PrimitiveSerialDescriptor("kotlinx.datetime.LocalDateTime", PrimitiveKind.STRING)
-
-    override fun deserialize(decoder: Decoder): LocalDateTime =
-        LocalDateTime.parse(decoder.decodeString())
-
-    override fun serialize(encoder: Encoder, value: LocalDateTime) {
-        encoder.encodeString(value.toString())
-    }
-
-}
+public object LocalDateTimeIso8601Serializer : KSerializer<LocalDateTime>
+by LocalDateTime.Formats.ISO.asKSerializer("kotlinx.datetime.LocalDateTime ISO")
 
 /**
  * A serializer for [LocalDateTime] that represents a value as its components.
@@ -40,7 +29,7 @@ public object LocalDateTimeIso8601Serializer: KSerializer<LocalDateTime> {
 public object LocalDateTimeComponentSerializer: KSerializer<LocalDateTime> {
 
     override val descriptor: SerialDescriptor =
-        buildClassSerialDescriptor("kotlinx.datetime.LocalDateTime") {
+        buildClassSerialDescriptor("kotlinx.datetime.LocalDateTime components") {
             element<Int>("year")
             element<Short>("month")
             element<Short>("day")
@@ -98,3 +87,54 @@ public object LocalDateTimeComponentSerializer: KSerializer<LocalDateTime> {
     }
 
 }
+
+/**
+ * An abstract serializer for [LocalDateTime] values that uses
+ * a custom [DateTimeFormat] to serialize and deserialize the value.
+ *
+ * [name] is the name of the serializer.
+ * The [SerialDescriptor.serialName] of the resulting serializer is `kotlinx.datetime.LocalDateTime serializer `[name].
+ * [SerialDescriptor.serialName] must be unique across all serializers in the same serialization context.
+ * When defining a serializer in a library, it is recommended to use the fully qualified class name in [name]
+ * to avoid conflicts with serializers defined by other libraries and client code.
+ *
+ * This serializer is abstract and must be subclassed to provide a concrete serializer.
+ * Example:
+ * ```
+ * // serializes LocalDateTime(2020, 1, 4, 12, 30) as the string "2020-01-04 12:30"
+ * object PythonDateTimeSerializer : FormattedLocalDateTimeSerializer("my.package.PythonDateTime",
+ *     LocalDateTime.Format {
+ *         date(LocalDate.Formats.ISO)
+ *         char(' ')
+ *         time(LocalTime.Formats.ISO)
+ *     }
+ * )
+ * ```
+ *
+ * Note that [LocalDateTime] is [kotlinx.serialization.Serializable] by default,
+ * so it is not necessary to create custom serializers when the format is not important.
+ * Additionally, [LocalDateTimeIso8601Serializer] is provided for the ISO 8601 format.
+ */
+public abstract class FormattedLocalDateTimeSerializer(
+    name: String, format: DateTimeFormat<LocalDateTime>
+) : KSerializer<LocalDateTime> by format.asKSerializer("kotlinx.datetime.LocalDateTime serializer $name")
+
+/**
+ * A serializer for [LocalDateTime] that uses the default [LocalDateTime.toString]/[LocalDateTime.parse].
+ *
+ * JSON example: `"2007-12-31T23:59:01"`
+ */
+@PublishedApi
+internal object LocalDateTimeSerializer: KSerializer<LocalDateTime> {
+
+    override val descriptor: SerialDescriptor =
+        PrimitiveSerialDescriptor("kotlinx.datetime.LocalDateTime", PrimitiveKind.STRING)
+
+    override fun deserialize(decoder: Decoder): LocalDateTime =
+        LocalDateTime.parse(decoder.decodeString())
+
+    override fun serialize(encoder: Encoder, value: LocalDateTime) {
+        encoder.encodeString(value.toString())
+    }
+
+}
diff --git a/core/common/src/serializers/LocalTimeSerializers.kt b/core/common/src/serializers/LocalTimeSerializers.kt
index b8c1c0eb..d67a6350 100644
--- a/core/common/src/serializers/LocalTimeSerializers.kt
+++ b/core/common/src/serializers/LocalTimeSerializers.kt
@@ -6,6 +6,7 @@
 package kotlinx.datetime.serializers
 
 import kotlinx.datetime.*
+import kotlinx.datetime.format.DateTimeFormat
 import kotlinx.serialization.*
 import kotlinx.serialization.descriptors.*
 import kotlinx.serialization.encoding.*
@@ -15,21 +16,10 @@ import kotlinx.serialization.encoding.*
  *
  * JSON example: `"12:01:03.999"`
  *
- * @see LocalDate.parse
- * @see LocalDate.toString
+ * @see LocalTime.Formats.ISO
  */
-public object LocalTimeIso8601Serializer : KSerializer<LocalTime> {
-
-    override val descriptor: SerialDescriptor =
-        PrimitiveSerialDescriptor("kotlinx.datetime.LocalTime", PrimitiveKind.STRING)
-
-    override fun deserialize(decoder: Decoder): LocalTime =
-        LocalTime.parse(decoder.decodeString())
-
-    override fun serialize(encoder: Encoder, value: LocalTime) {
-        encoder.encodeString(value.toString())
-    }
-}
+public object LocalTimeIso8601Serializer : KSerializer<LocalTime>
+by LocalTime.Formats.ISO.asKSerializer("kotlinx.datetime.LocalTime ISO")
 
 /**
  * A serializer for [LocalTime] that represents a value as its components.
@@ -39,7 +29,7 @@ public object LocalTimeIso8601Serializer : KSerializer<LocalTime> {
 public object LocalTimeComponentSerializer : KSerializer<LocalTime> {
 
     override val descriptor: SerialDescriptor =
-        buildClassSerialDescriptor("kotlinx.datetime.LocalTime") {
+        buildClassSerialDescriptor("kotlinx.datetime.LocalTime components") {
             element<Short>("hour")
             element<Short>("minute")
             element<Short>("second", isOptional = true)
@@ -81,3 +71,52 @@ public object LocalTimeComponentSerializer : KSerializer<LocalTime> {
         }
     }
 }
+
+/**
+ * An abstract serializer for [LocalTime] values that uses
+ * a custom [DateTimeFormat] to serialize and deserialize the value.
+ *
+ * [name] is the name of the serializer.
+ * The [SerialDescriptor.serialName] of the resulting serializer is `kotlinx.datetime.LocalTime serializer `[name].
+ * [SerialDescriptor.serialName] must be unique across all serializers in the same serialization context.
+ * When defining a serializer in a library, it is recommended to use the fully qualified class name in [name]
+ * to avoid conflicts with serializers defined by other libraries and client code.
+ *
+ * This serializer is abstract and must be subclassed to provide a concrete serializer.
+ * Example:
+ * ```
+ * // serializes LocalTime(12, 30) as "12:30:00.000"
+ * object FixedWidthTimeSerializer : FormattedLocalTimeSerializer("my.package.FixedWidthTime", LocalTime.Format {
+ *     hour(); char(':'); minute(); char(':'); second(); char('.'); secondFraction(3)
+ * })
+ * ```
+ *
+ * Note that [LocalTime] is [kotlinx.serialization.Serializable] by default,
+ * so it is not necessary to create custom serializers when the format is not important.
+ * Additionally, [LocalTimeIso8601Serializer] is provided for the ISO 8601 format.
+ */
+public abstract class FormattedLocalTimeSerializer(
+    name: String, format: DateTimeFormat<LocalTime>
+) : KSerializer<LocalTime> by format.asKSerializer("kotlinx.datetime.LocalTime serializer $name")
+
+/**
+ * A serializer for [LocalTime] that uses the ISO 8601 representation.
+ *
+ * JSON example: `"12:01:03.999"`
+ *
+ * @see LocalDate.parse
+ * @see LocalDate.toString
+ */
+@PublishedApi
+internal object LocalTimeSerializer : KSerializer<LocalTime> {
+
+    override val descriptor: SerialDescriptor =
+        PrimitiveSerialDescriptor("kotlinx.datetime.LocalTime", PrimitiveKind.STRING)
+
+    override fun deserialize(decoder: Decoder): LocalTime =
+        LocalTime.parse(decoder.decodeString())
+
+    override fun serialize(encoder: Encoder, value: LocalTime) {
+        encoder.encodeString(value.toString())
+    }
+}
diff --git a/core/common/src/serializers/TimeZoneSerializers.kt b/core/common/src/serializers/TimeZoneSerializers.kt
index 2d6d1c38..538aee5b 100644
--- a/core/common/src/serializers/TimeZoneSerializers.kt
+++ b/core/common/src/serializers/TimeZoneSerializers.kt
@@ -5,9 +5,8 @@
 
 package kotlinx.datetime.serializers
 
-import kotlinx.datetime.FixedOffsetTimeZone
-import kotlinx.datetime.TimeZone
-import kotlinx.datetime.UtcOffset
+import kotlinx.datetime.*
+import kotlinx.datetime.format.DateTimeFormat
 import kotlinx.serialization.*
 import kotlinx.serialization.descriptors.*
 import kotlinx.serialization.encoding.*
@@ -58,9 +57,17 @@ public object FixedOffsetTimeZoneSerializer: KSerializer<FixedOffsetTimeZone> {
  *
  * JSON example: `"+02:00"`
  *
- * @see UtcOffset.parse
- * @see UtcOffset.toString
+ * @see UtcOffset.Formats.ISO
  */
+public object UtcOffsetIso8601Serializer : KSerializer<UtcOffset>
+by UtcOffset.Formats.ISO.asKSerializer("kotlinx.datetime.UtcOffset ISO")
+
+/**
+ * A serializer for [UtcOffset] that uses the default [UtcOffset.toString]/[UtcOffset.parse].
+ *
+ * JSON example: `"+02:00"`
+ */
+@Deprecated("Use UtcOffset.serializer() instead", ReplaceWith("UtcOffset.serializer()"))
 public object UtcOffsetSerializer: KSerializer<UtcOffset> {
 
     override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("kotlinx.datetime.UtcOffset", PrimitiveKind.STRING)
@@ -74,3 +81,30 @@ public object UtcOffsetSerializer: KSerializer<UtcOffset> {
     }
 
 }
+
+/**
+ * An abstract serializer for [UtcOffset] values that uses
+ * a custom [DateTimeFormat] to serialize and deserialize the value.
+ *
+ * [name] is the name of the serializer.
+ * The [SerialDescriptor.serialName] of the resulting serializer is `kotlinx.datetime.UtcOffset serializer `[name].
+ * [SerialDescriptor.serialName] must be unique across all serializers in the same serialization context.
+ * When defining a serializer in a library, it is recommended to use the fully qualified class name in [name]
+ * to avoid conflicts with serializers defined by other libraries and client code.
+ *
+ * This serializer is abstract and must be subclassed to provide a concrete serializer.
+ * Example:
+ * ```
+ * // serializes the UTC offset UtcOffset(hours = 2) as the string "+0200"
+ * object FourDigitOffsetSerializer : FormattedUtcOffsetSerializer(
+ *     "my.package.FOUR_DIGITS", UtcOffset.Formats.FOUR_DIGITS
+ * )
+ * ```
+ *
+ * Note that [UtcOffset] is [kotlinx.serialization.Serializable] by default,
+ * so it is not necessary to create custom serializers when the format is not important.
+ * Additionally, [UtcOffsetSerializer] is provided for the ISO 8601 format.
+ */
+public abstract class FormattedUtcOffsetSerializer(
+    name: String, format: DateTimeFormat<UtcOffset>
+) : KSerializer<UtcOffset> by format.asKSerializer("kotlinx.datetime.UtcOffset serializer $name")
diff --git a/core/commonJs/src/Instant.kt b/core/commonJs/src/Instant.kt
index af7cc868..45c6c2f8 100644
--- a/core/commonJs/src/Instant.kt
+++ b/core/commonJs/src/Instant.kt
@@ -13,13 +13,13 @@ import kotlinx.datetime.internal.JSJoda.ChronoUnit as jtChronoUnit
 import kotlinx.datetime.internal.JSJoda.ZonedDateTime as jtZonedDateTime
 import kotlinx.datetime.internal.safeAdd
 import kotlinx.datetime.internal.*
-import kotlinx.datetime.serializers.InstantIso8601Serializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 import kotlin.time.*
 import kotlin.time.Duration.Companion.nanoseconds
 import kotlin.time.Duration.Companion.seconds
 
-@Serializable(with = InstantIso8601Serializer::class)
+@Serializable(with = InstantSerializer::class)
 public actual class Instant internal constructor(internal val value: jtInstant) : Comparable<Instant> {
 
     public actual val epochSeconds: Long
diff --git a/core/commonJs/src/LocalDate.kt b/core/commonJs/src/LocalDate.kt
index a650665d..2f6285cb 100644
--- a/core/commonJs/src/LocalDate.kt
+++ b/core/commonJs/src/LocalDate.kt
@@ -6,12 +6,12 @@
 package kotlinx.datetime
 
 import kotlinx.datetime.format.*
-import kotlinx.datetime.serializers.LocalDateIso8601Serializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 import kotlinx.datetime.internal.JSJoda.LocalDate as jtLocalDate
 import kotlinx.datetime.internal.JSJoda.ChronoUnit as jtChronoUnit
 
-@Serializable(with = LocalDateIso8601Serializer::class)
+@Serializable(with = LocalDateSerializer::class)
 public actual class LocalDate internal constructor(internal val value: jtLocalDate) : Comparable<LocalDate> {
     public actual companion object {
 
diff --git a/core/commonJs/src/LocalDateTime.kt b/core/commonJs/src/LocalDateTime.kt
index c85e772a..59dfaaab 100644
--- a/core/commonJs/src/LocalDateTime.kt
+++ b/core/commonJs/src/LocalDateTime.kt
@@ -7,11 +7,11 @@ package kotlinx.datetime
 import kotlinx.datetime.format.*
 import kotlinx.datetime.format.ISO_DATETIME
 import kotlinx.datetime.format.LocalDateTimeFormat
-import kotlinx.datetime.serializers.LocalDateTimeIso8601Serializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 import kotlinx.datetime.internal.JSJoda.LocalDateTime as jtLocalDateTime
 
-@Serializable(with = LocalDateTimeIso8601Serializer::class)
+@Serializable(with = LocalDateTimeSerializer::class)
 public actual class LocalDateTime internal constructor(internal val value: jtLocalDateTime) : Comparable<LocalDateTime> {
 
     public actual constructor(year: Int, monthNumber: Int, dayOfMonth: Int, hour: Int, minute: Int, second: Int, nanosecond: Int) :
diff --git a/core/commonJs/src/LocalTime.kt b/core/commonJs/src/LocalTime.kt
index 674e5cb6..72aab223 100644
--- a/core/commonJs/src/LocalTime.kt
+++ b/core/commonJs/src/LocalTime.kt
@@ -8,11 +8,11 @@ import kotlinx.datetime.format.*
 import kotlinx.datetime.format.ISO_TIME
 import kotlinx.datetime.format.LocalTimeFormat
 import kotlinx.datetime.internal.*
-import kotlinx.datetime.serializers.LocalTimeIso8601Serializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 import kotlinx.datetime.internal.JSJoda.LocalTime as jtLocalTime
 
-@Serializable(LocalTimeIso8601Serializer::class)
+@Serializable(LocalTimeSerializer::class)
 public actual class LocalTime internal constructor(internal val value: jtLocalTime) :
     Comparable<LocalTime> {
 
diff --git a/core/commonJs/src/UtcOffset.kt b/core/commonJs/src/UtcOffset.kt
index 65dcf865..8f0ed74e 100644
--- a/core/commonJs/src/UtcOffset.kt
+++ b/core/commonJs/src/UtcOffset.kt
@@ -11,9 +11,10 @@ import kotlinx.datetime.internal.JSJoda.DateTimeFormatterBuilder as jtDateTimeFo
 import kotlinx.datetime.internal.JSJoda.DateTimeFormatter as jtDateTimeFormatter
 import kotlinx.datetime.internal.JSJoda.ResolverStyle as jtResolverStyle
 import kotlinx.datetime.format.*
-import kotlinx.datetime.serializers.UtcOffsetSerializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 
+@Suppress("DEPRECATION")
 @Serializable(with = UtcOffsetSerializer::class)
 public actual class UtcOffset internal constructor(internal val zoneOffset: jtZoneOffset) {
     public actual val totalSeconds: Int get() = zoneOffset.totalSeconds()
diff --git a/core/jvm/src/Instant.kt b/core/jvm/src/Instant.kt
index ab347464..b7783206 100644
--- a/core/jvm/src/Instant.kt
+++ b/core/jvm/src/Instant.kt
@@ -9,7 +9,7 @@ package kotlinx.datetime
 import kotlinx.datetime.format.*
 import kotlinx.datetime.internal.safeMultiply
 import kotlinx.datetime.internal.*
-import kotlinx.datetime.serializers.InstantIso8601Serializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 import java.time.DateTimeException
 import java.time.temporal.*
@@ -19,7 +19,7 @@ import kotlin.time.Duration.Companion.seconds
 import java.time.Instant as jtInstant
 import java.time.Clock as jtClock
 
-@Serializable(with = InstantIso8601Serializer::class)
+@Serializable(with = InstantSerializer::class)
 public actual class Instant internal constructor(internal val value: jtInstant) : Comparable<Instant> {
 
     public actual val epochSeconds: Long
diff --git a/core/jvm/src/LocalDate.kt b/core/jvm/src/LocalDate.kt
index fe3b9ae1..c0d2be84 100644
--- a/core/jvm/src/LocalDate.kt
+++ b/core/jvm/src/LocalDate.kt
@@ -9,14 +9,14 @@ import kotlinx.datetime.format.*
 import kotlinx.datetime.internal.safeAdd
 import kotlinx.datetime.internal.safeMultiply
 import kotlinx.datetime.internal.*
-import kotlinx.datetime.serializers.LocalDateIso8601Serializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 import java.time.DateTimeException
 import java.time.format.DateTimeParseException
 import java.time.temporal.ChronoUnit
 import java.time.LocalDate as jtLocalDate
 
-@Serializable(with = LocalDateIso8601Serializer::class)
+@Serializable(with = LocalDateSerializer::class)
 public actual class LocalDate internal constructor(internal val value: jtLocalDate) : Comparable<LocalDate> {
     public actual companion object {
         public actual fun parse(input: CharSequence, format: DateTimeFormat<LocalDate>): LocalDate =
diff --git a/core/jvm/src/LocalDateTime.kt b/core/jvm/src/LocalDateTime.kt
index 7dc28cdb..54f2b3de 100644
--- a/core/jvm/src/LocalDateTime.kt
+++ b/core/jvm/src/LocalDateTime.kt
@@ -6,7 +6,7 @@
 package kotlinx.datetime
 
 import kotlinx.datetime.format.*
-import kotlinx.datetime.serializers.LocalDateTimeIso8601Serializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 import java.time.DateTimeException
 import java.time.format.DateTimeParseException
@@ -15,7 +15,7 @@ import java.time.LocalDateTime as jtLocalDateTime
 public actual typealias Month = java.time.Month
 public actual typealias DayOfWeek = java.time.DayOfWeek
 
-@Serializable(with = LocalDateTimeIso8601Serializer::class)
+@Serializable(with = LocalDateTimeSerializer::class)
 public actual class LocalDateTime internal constructor(internal val value: jtLocalDateTime) : Comparable<LocalDateTime> {
 
     public actual constructor(year: Int, monthNumber: Int, dayOfMonth: Int, hour: Int, minute: Int, second: Int, nanosecond: Int) :
diff --git a/core/jvm/src/LocalTime.kt b/core/jvm/src/LocalTime.kt
index 71052570..fe67736d 100644
--- a/core/jvm/src/LocalTime.kt
+++ b/core/jvm/src/LocalTime.kt
@@ -8,13 +8,13 @@ package kotlinx.datetime
 
 import kotlinx.datetime.format.*
 import kotlinx.datetime.internal.*
-import kotlinx.datetime.serializers.LocalTimeIso8601Serializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 import java.time.DateTimeException
 import java.time.format.DateTimeParseException
 import java.time.LocalTime as jtLocalTime
 
-@Serializable(with = LocalTimeIso8601Serializer::class)
+@Serializable(with = LocalTimeSerializer::class)
 public actual class LocalTime internal constructor(internal val value: jtLocalTime) :
     Comparable<LocalTime> {
 
diff --git a/core/jvm/src/UtcOffsetJvm.kt b/core/jvm/src/UtcOffsetJvm.kt
index 129857d7..aa02495c 100644
--- a/core/jvm/src/UtcOffsetJvm.kt
+++ b/core/jvm/src/UtcOffsetJvm.kt
@@ -6,13 +6,14 @@
 package kotlinx.datetime
 
 import kotlinx.datetime.format.*
-import kotlinx.datetime.serializers.UtcOffsetSerializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 import java.time.DateTimeException
 import java.time.ZoneOffset
 import java.time.format.DateTimeFormatterBuilder
 import java.time.format.*
 
+@Suppress("DEPRECATION")
 @Serializable(with = UtcOffsetSerializer::class)
 public actual class UtcOffset(internal val zoneOffset: ZoneOffset) {
     public actual val totalSeconds: Int get() = zoneOffset.totalSeconds
diff --git a/core/native/src/Instant.kt b/core/native/src/Instant.kt
index 70e0017b..96185694 100644
--- a/core/native/src/Instant.kt
+++ b/core/native/src/Instant.kt
@@ -10,7 +10,7 @@ package kotlinx.datetime
 
 import kotlinx.datetime.format.*
 import kotlinx.datetime.internal.*
-import kotlinx.datetime.serializers.InstantIso8601Serializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 import kotlin.time.*
 import kotlin.time.Duration.Companion.nanoseconds
@@ -38,7 +38,7 @@ private const val MAX_SECOND = 31494816403199L // +1000000-12-31T23:59:59
 
 private fun isValidInstantSecond(second: Long) = second >= MIN_SECOND && second <= MAX_SECOND
 
-@Serializable(with = InstantIso8601Serializer::class)
+@Serializable(with = InstantSerializer::class)
 public actual class Instant internal constructor(public actual val epochSeconds: Long, public actual val nanosecondsOfSecond: Int) : Comparable<Instant> {
 
     init {
diff --git a/core/native/src/LocalDate.kt b/core/native/src/LocalDate.kt
index 14ee3a17..714bbebf 100644
--- a/core/native/src/LocalDate.kt
+++ b/core/native/src/LocalDate.kt
@@ -12,7 +12,7 @@ import kotlinx.datetime.format.*
 import kotlinx.datetime.internal.*
 import kotlinx.datetime.internal.safeAdd
 import kotlinx.datetime.internal.safeMultiply
-import kotlinx.datetime.serializers.LocalDateIso8601Serializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 import kotlin.math.*
 
@@ -22,7 +22,7 @@ internal const val YEAR_MAX = 999_999
 private fun isValidYear(year: Int): Boolean =
     year >= YEAR_MIN && year <= YEAR_MAX
 
-@Serializable(with = LocalDateIso8601Serializer::class)
+@Serializable(with = LocalDateSerializer::class)
 public actual class LocalDate actual constructor(public actual val year: Int, public actual val monthNumber: Int, public actual val dayOfMonth: Int) : Comparable<LocalDate> {
 
     init {
diff --git a/core/native/src/LocalDateTime.kt b/core/native/src/LocalDateTime.kt
index 33187d4a..3b58e470 100644
--- a/core/native/src/LocalDateTime.kt
+++ b/core/native/src/LocalDateTime.kt
@@ -13,7 +13,7 @@ import kotlinx.datetime.internal.*
 import kotlinx.datetime.serializers.*
 import kotlinx.serialization.*
 
-@Serializable(with = LocalDateTimeIso8601Serializer::class)
+@Serializable(with = LocalDateTimeSerializer::class)
 public actual class LocalDateTime
 public actual constructor(public actual val date: LocalDate, public actual val time: LocalTime) : Comparable<LocalDateTime> {
     public actual companion object {
diff --git a/core/native/src/LocalTime.kt b/core/native/src/LocalTime.kt
index 28ebd78d..42f5c017 100644
--- a/core/native/src/LocalTime.kt
+++ b/core/native/src/LocalTime.kt
@@ -10,10 +10,10 @@ package kotlinx.datetime
 
 import kotlinx.datetime.internal.*
 import kotlinx.datetime.format.*
-import kotlinx.datetime.serializers.LocalTimeIso8601Serializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 
-@Serializable(LocalTimeIso8601Serializer::class)
+@Serializable(LocalTimeSerializer::class)
 public actual class LocalTime actual constructor(
     public actual val hour: Int,
     public actual val minute: Int,
diff --git a/core/native/src/UtcOffset.kt b/core/native/src/UtcOffset.kt
index abe8c64d..6213360b 100644
--- a/core/native/src/UtcOffset.kt
+++ b/core/native/src/UtcOffset.kt
@@ -7,10 +7,11 @@ package kotlinx.datetime
 
 import kotlinx.datetime.internal.*
 import kotlinx.datetime.format.*
-import kotlinx.datetime.serializers.UtcOffsetSerializer
+import kotlinx.datetime.serializers.*
 import kotlinx.serialization.Serializable
 import kotlin.math.abs
 
+@Suppress("DEPRECATION")
 @Serializable(with = UtcOffsetSerializer::class)
 public actual class UtcOffset private constructor(public actual val totalSeconds: Int) {
 
diff --git a/serialization/common/test/DateTimePeriodSerializationTest.kt b/serialization/common/test/DateTimePeriodSerializationTest.kt
index a8cb1a6c..9869d424 100644
--- a/serialization/common/test/DateTimePeriodSerializationTest.kt
+++ b/serialization/common/test/DateTimePeriodSerializationTest.kt
@@ -97,28 +97,34 @@ class DateTimePeriodSerializationTest {
 
     @Test
     fun testDatePeriodIso8601Serialization() {
+        assertKSerializerName("kotlinx.datetime.DatePeriod ISO", DatePeriodIso8601Serializer)
         datePeriodIso8601Serialization(DatePeriodIso8601Serializer, DateTimePeriodIso8601Serializer)
     }
 
     @Test
     fun testDatePeriodComponentSerialization() {
+        assertKSerializerName("kotlinx.datetime.DatePeriod components", DatePeriodComponentSerializer)
         datePeriodComponentSerialization(DatePeriodComponentSerializer, DateTimePeriodComponentSerializer)
     }
 
     @Test
     fun testDateTimePeriodIso8601Serialization() {
+        assertKSerializerName("kotlinx.datetime.DateTimePeriod ISO", DateTimePeriodIso8601Serializer)
         dateTimePeriodIso8601Serialization(DateTimePeriodIso8601Serializer)
     }
 
     @Test
     fun testDateTimePeriodComponentSerialization() {
+        assertKSerializerName("kotlinx.datetime.DateTimePeriod components", DateTimePeriodComponentSerializer)
         dateTimePeriodComponentSerialization(DateTimePeriodComponentSerializer)
     }
 
     @Test
     fun testDefaultSerializers() {
         // Check that they behave the same as the ISO 8601 serializers
+        assertKSerializerName<DateTimePeriod>("kotlinx.datetime.DateTimePeriod", Json.serializersModule.serializer())
         dateTimePeriodIso8601Serialization(Json.serializersModule.serializer())
+        assertKSerializerName<DatePeriod>("kotlinx.datetime.DatePeriod", Json.serializersModule.serializer())
         datePeriodIso8601Serialization(Json.serializersModule.serializer(), Json.serializersModule.serializer())
     }
 
diff --git a/serialization/common/test/DateTimeUnitSerializationTest.kt b/serialization/common/test/DateTimeUnitSerializationTest.kt
index e2b4f8b6..39e57a25 100644
--- a/serialization/common/test/DateTimeUnitSerializationTest.kt
+++ b/serialization/common/test/DateTimeUnitSerializationTest.kt
@@ -18,7 +18,7 @@ class DateTimeUnitSerializationTest {
         repeat(100) {
             val nanoseconds = Random.nextLong(1, Long.MAX_VALUE)
             val unit = DateTimeUnit.TimeBased(nanoseconds)
-            val json = "{\"nanoseconds\":${nanoseconds.toString()}}" // https://youtrack.jetbrains.com/issue/KT-39891
+            val json = "{\"nanoseconds\":$nanoseconds}"
             assertEquals(json, Json.encodeToString(serializer, unit))
             assertEquals(unit, Json.decodeFromString(serializer, json))
         }
@@ -65,7 +65,7 @@ class DateTimeUnitSerializationTest {
         repeat(100) {
             val nanoseconds = Random.nextLong(1, Long.MAX_VALUE)
             val unit = DateTimeUnit.TimeBased(nanoseconds)
-            val json = "{\"type\":\"kotlinx.datetime.TimeBased\",\"nanoseconds\":${nanoseconds.toString()}}" // https://youtrack.jetbrains.com/issue/KT-39891
+            val json = "{\"type\":\"kotlinx.datetime.TimeBased\",\"nanoseconds\":$nanoseconds}"
             assertEquals(json, Json.encodeToString(serializer, unit))
             assertEquals(unit, Json.decodeFromString(serializer, json))
         }
@@ -87,21 +87,25 @@ class DateTimeUnitSerializationTest {
 
     @Test
     fun testTimeBasedUnitSerialization() {
+        assertKSerializerName("kotlinx.datetime.TimeBased", TimeBasedDateTimeUnitSerializer)
         timeBasedSerialization(TimeBasedDateTimeUnitSerializer)
     }
 
     @Test
     fun testDayBasedSerialization() {
+        assertKSerializerName("kotlinx.datetime.DayBased", DayBasedDateTimeUnitSerializer)
         dayBasedSerialization(DayBasedDateTimeUnitSerializer)
     }
 
     @Test
     fun testMonthBasedSerialization() {
+        assertKSerializerName("kotlinx.datetime.MonthBased", MonthBasedDateTimeUnitSerializer)
         monthBasedSerialization(MonthBasedDateTimeUnitSerializer)
     }
 
     @Test
     fun testDateBasedSerialization() {
+        assertKSerializerName("kotlinx.datetime.DateTimeUnit.DateBased", DateBasedDateTimeUnitSerializer)
         dateBasedSerialization(DateBasedDateTimeUnitSerializer)
     }
 
diff --git a/serialization/common/test/DayOfWeekSerializationTest.kt b/serialization/common/test/DayOfWeekSerializationTest.kt
index aa81e8ac..70eb35a9 100644
--- a/serialization/common/test/DayOfWeekSerializationTest.kt
+++ b/serialization/common/test/DayOfWeekSerializationTest.kt
@@ -13,10 +13,11 @@ import kotlin.test.*
 class DayOfWeekSerializationTest {
     @Test
     fun testSerialization() {
+        assertKSerializerName("kotlinx.datetime.DayOfWeek", DayOfWeekSerializer)
         for (dayOfWeek in DayOfWeek.entries) {
             val json = "\"${dayOfWeek.name}\""
             assertEquals(json, Json.encodeToString(DayOfWeekSerializer, dayOfWeek))
             assertEquals(dayOfWeek, Json.decodeFromString(DayOfWeekSerializer, json))
         }
     }
-}
\ No newline at end of file
+}
diff --git a/serialization/common/test/InstantSerializationTest.kt b/serialization/common/test/InstantSerializationTest.kt
index dea5c2db..d7a18a2b 100644
--- a/serialization/common/test/InstantSerializationTest.kt
+++ b/serialization/common/test/InstantSerializationTest.kt
@@ -5,6 +5,7 @@
 package kotlinx.datetime.serialization.test
 
 import kotlinx.datetime.*
+import kotlinx.datetime.format.DateTimeComponents
 import kotlinx.datetime.serializers.*
 import kotlinx.serialization.*
 import kotlinx.serialization.json.*
@@ -14,10 +15,26 @@ class InstantSerializationTest {
 
     private fun iso8601Serialization(serializer: KSerializer<Instant>) {
         for ((instant, json) in listOf(
-            Pair(Instant.fromEpochSeconds(1607505416, 124000),
-                "\"2020-12-09T09:16:56.000124Z\""),
-            Pair(Instant.fromEpochSeconds(-1607505416, -124000),
-                "\"1919-01-23T14:43:03.999876Z\""),
+            Pair(Instant.fromEpochSeconds(1607505416, 120000),
+                "\"2020-12-09T09:16:56.00012Z\""),
+            Pair(Instant.fromEpochSeconds(-1607505416, -120000),
+                "\"1919-01-23T14:43:03.99988Z\""),
+            Pair(Instant.fromEpochSeconds(987654321, 123456789),
+                "\"2001-04-19T04:25:21.123456789Z\""),
+            Pair(Instant.fromEpochSeconds(987654321, 0),
+                "\"2001-04-19T04:25:21Z\""),
+        )) {
+            assertEquals(json, Json.encodeToString(serializer, instant))
+            assertEquals(instant, Json.decodeFromString(serializer, json))
+        }
+    }
+
+    private fun defaultSerialization(serializer: KSerializer<Instant>) {
+        for ((instant, json) in listOf(
+            Pair(Instant.fromEpochSeconds(1607505416, 120000),
+                "\"2020-12-09T09:16:56.000120Z\""),
+            Pair(Instant.fromEpochSeconds(-1607505416, -120000),
+                "\"1919-01-23T14:43:03.999880Z\""),
             Pair(Instant.fromEpochSeconds(987654321, 123456789),
                 "\"2001-04-19T04:25:21.123456789Z\""),
             Pair(Instant.fromEpochSeconds(987654321, 0),
@@ -53,17 +70,42 @@ class InstantSerializationTest {
 
     @Test
     fun testIso8601Serialization() {
+        assertKSerializerName("kotlinx.datetime.Instant ISO", InstantIso8601Serializer)
         iso8601Serialization(InstantIso8601Serializer)
     }
 
     @Test
     fun testComponentSerialization() {
+        assertKSerializerName("kotlinx.datetime.Instant components", InstantComponentSerializer)
         componentSerialization(InstantComponentSerializer)
     }
 
     @Test
     fun testDefaultSerializers() {
         // should be the same as the ISO 8601
-        iso8601Serialization(Json.serializersModule.serializer())
+        assertKSerializerName<Instant>("kotlinx.datetime.Instant", Json.serializersModule.serializer())
+        defaultSerialization(Json.serializersModule.serializer())
+    }
+
+    object Rfc1123InstantSerializer : FormattedInstantSerializer("RFC_1123", DateTimeComponents.Formats.RFC_1123)
+
+    @Test
+    fun testCustomSerializer() {
+        assertKSerializerName("kotlinx.datetime.Instant serializer RFC_1123", Rfc1123InstantSerializer)
+        for ((instant, json) in listOf(
+            Pair(Instant.fromEpochSeconds(1607505416),
+                "\"Wed, 9 Dec 2020 09:16:56 GMT\""),
+            Pair(Instant.fromEpochSeconds(-1607505416),
+                "\"Thu, 23 Jan 1919 14:43:04 GMT\""),
+            Pair(Instant.fromEpochSeconds(987654321),
+                "\"Thu, 19 Apr 2001 04:25:21 GMT\""),
+        )) {
+            assertEquals(json, Json.encodeToString(Rfc1123InstantSerializer, instant))
+            assertEquals(instant, Json.decodeFromString(Rfc1123InstantSerializer, json))
+        }
+        assertEquals("\"Thu, 19 Apr 2001 04:25:21 GMT\"",
+            Json.encodeToString(Rfc1123InstantSerializer, Instant.fromEpochSeconds(987654321, 123456789)))
+        assertEquals(Instant.fromEpochSeconds(987654321),
+            Json.decodeFromString(Rfc1123InstantSerializer, "\"Thu, 19 Apr 2001 08:25:21 +0400\""))
     }
 }
diff --git a/serialization/common/test/LocalDateSerializationTest.kt b/serialization/common/test/LocalDateSerializationTest.kt
index 91ed3827..420c4db4 100644
--- a/serialization/common/test/LocalDateSerializationTest.kt
+++ b/serialization/common/test/LocalDateSerializationTest.kt
@@ -56,18 +56,40 @@ class LocalDateSerializationTest {
 
     @Test
     fun testIso8601Serialization() {
+        assertKSerializerName("kotlinx.datetime.LocalDate ISO", LocalDateIso8601Serializer)
         iso8601Serialization(LocalDateIso8601Serializer)
     }
 
     @Test
     fun testComponentSerialization() {
+        assertKSerializerName("kotlinx.datetime.LocalDate components", LocalDateComponentSerializer)
         componentSerialization(LocalDateComponentSerializer)
     }
 
     @Test
     fun testDefaultSerializers() {
         // should be the same as the ISO 8601
+        assertKSerializerName<LocalDate>("kotlinx.datetime.LocalDate", Json.serializersModule.serializer())
         iso8601Serialization(Json.serializersModule.serializer())
     }
 
+    object IsoBasicLocalDateSerializer : FormattedLocalDateSerializer("ISO_BASIC", LocalDate.Formats.ISO_BASIC)
+
+    @Test
+    fun testCustomSerializer() {
+        assertKSerializerName("kotlinx.datetime.LocalDate serializer ISO_BASIC", IsoBasicLocalDateSerializer)
+        for ((localDate, json) in listOf(
+            Pair(LocalDate(2020, 12, 9), "\"20201209\""),
+            Pair(LocalDate(-2020, 1, 1), "\"-20200101\""),
+            Pair(LocalDate(2019, 10, 1), "\"20191001\""),
+        )) {
+            assertEquals(json, Json.encodeToString(IsoBasicLocalDateSerializer, localDate))
+            assertEquals(localDate, Json.decodeFromString(IsoBasicLocalDateSerializer, json))
+        }
+    }
+}
+
+@OptIn(ExperimentalSerializationApi::class)
+fun <T> assertKSerializerName(expectedName: String, serializer: KSerializer<T>) {
+    assertEquals(expectedName, serializer.descriptor.serialName)
 }
diff --git a/serialization/common/test/LocalDateTimeSerializationTest.kt b/serialization/common/test/LocalDateTimeSerializationTest.kt
index c01e647c..aede7abb 100644
--- a/serialization/common/test/LocalDateTimeSerializationTest.kt
+++ b/serialization/common/test/LocalDateTimeSerializationTest.kt
@@ -6,6 +6,7 @@
 package kotlinx.datetime.serialization.test
 
 import kotlinx.datetime.*
+import kotlinx.datetime.format.char
 import kotlinx.datetime.serializers.*
 import kotlinx.serialization.KSerializer
 import kotlinx.serialization.json.*
@@ -14,6 +15,19 @@ import kotlin.test.*
 
 class LocalDateTimeSerializationTest {
     private fun iso8601Serialization(serializer: KSerializer<LocalDateTime>) {
+        for ((localDateTime, json) in listOf(
+            Pair(LocalDateTime(2008, 7, 5, 2, 1), "\"2008-07-05T02:01:00\""),
+            Pair(LocalDateTime(2007, 12, 31, 23, 59, 1), "\"2007-12-31T23:59:01\""),
+            Pair(LocalDateTime(999, 12, 31, 23, 59, 59, 990000000), "\"0999-12-31T23:59:59.99\""),
+            Pair(LocalDateTime(-1, 1, 2, 23, 59, 59, 999990000), "\"-0001-01-02T23:59:59.99999\""),
+            Pair(LocalDateTime(-2008, 1, 2, 23, 59, 59, 999999990), "\"-2008-01-02T23:59:59.99999999\""),
+        )) {
+            assertEquals(json, Json.encodeToString(serializer, localDateTime))
+            assertEquals(localDateTime, Json.decodeFromString(serializer, json))
+        }
+    }
+
+    private fun defaultSerialization(serializer: KSerializer<LocalDateTime>) {
         for ((localDateTime, json) in listOf(
             Pair(LocalDateTime(2008, 7, 5, 2, 1), "\"2008-07-05T02:01\""),
             Pair(LocalDateTime(2007, 12, 31, 23, 59, 1), "\"2007-12-31T23:59:01\""),
@@ -69,17 +83,43 @@ class LocalDateTimeSerializationTest {
 
     @Test
     fun testIso8601Serialization() {
+        assertKSerializerName<LocalDateTime>("kotlinx.datetime.LocalDateTime ISO", LocalDateTimeIso8601Serializer)
         iso8601Serialization(LocalDateTimeIso8601Serializer)
     }
 
     @Test
     fun testComponentSerialization() {
+        assertKSerializerName<LocalDateTime>(
+            "kotlinx.datetime.LocalDateTime components", LocalDateTimeComponentSerializer
+        )
         componentSerialization(LocalDateTimeComponentSerializer)
     }
 
     @Test
     fun testDefaultSerializers() {
         // should be the same as the ISO 8601
-        iso8601Serialization(Json.serializersModule.serializer())
+        assertKSerializerName<LocalDateTime>("kotlinx.datetime.LocalDateTime", Json.serializersModule.serializer())
+        defaultSerialization(Json.serializersModule.serializer())
+    }
+
+    object PythonDateTimeSerializer : FormattedLocalDateTimeSerializer("PythonDateTime", LocalDateTime.Format {
+        date(LocalDate.Formats.ISO)
+        char(' ')
+        time(LocalTime.Formats.ISO)
+    })
+
+    @Test
+    fun testCustomSerializer() {
+        assertKSerializerName("kotlinx.datetime.LocalDateTime serializer PythonDateTime", PythonDateTimeSerializer)
+        for ((localDateTime, json) in listOf(
+            Pair(LocalDateTime(2008, 7, 5, 2, 1), "\"2008-07-05 02:01:00\""),
+            Pair(LocalDateTime(2007, 12, 31, 23, 59, 1), "\"2007-12-31 23:59:01\""),
+            Pair(LocalDateTime(999, 12, 31, 23, 59, 59, 990000000), "\"0999-12-31 23:59:59.99\""),
+            Pair(LocalDateTime(-1, 1, 2, 23, 59, 59, 999990000), "\"-0001-01-02 23:59:59.99999\""),
+            Pair(LocalDateTime(-2008, 1, 2, 23, 59, 59, 999999990), "\"-2008-01-02 23:59:59.99999999\""),
+        )) {
+            assertEquals(json, Json.encodeToString(PythonDateTimeSerializer, localDateTime))
+            assertEquals(localDateTime, Json.decodeFromString(PythonDateTimeSerializer, json))
+        }
     }
 }
diff --git a/serialization/common/test/LocalTimeSerializationTest.kt b/serialization/common/test/LocalTimeSerializationTest.kt
index 5df81f54..c7d44b40 100644
--- a/serialization/common/test/LocalTimeSerializationTest.kt
+++ b/serialization/common/test/LocalTimeSerializationTest.kt
@@ -6,6 +6,7 @@
 package kotlinx.datetime.serialization.test
 
 import kotlinx.datetime.*
+import kotlinx.datetime.format.char
 import kotlinx.datetime.serializers.*
 import kotlinx.serialization.KSerializer
 import kotlinx.serialization.json.*
@@ -14,6 +15,19 @@ import kotlin.test.*
 
 class LocalTimeSerializationTest {
     private fun iso8601Serialization(serializer: KSerializer<LocalTime>) {
+        for ((localTime, json) in listOf(
+            Pair(LocalTime(2, 1), "\"02:01:00\""),
+            Pair(LocalTime(23, 59, 1), "\"23:59:01\""),
+            Pair(LocalTime(23, 59, 59, 990000000), "\"23:59:59.99\""),
+            Pair(LocalTime(23, 59, 59, 999990000), "\"23:59:59.99999\""),
+            Pair(LocalTime(23, 59, 59, 999999990), "\"23:59:59.99999999\""),
+        )) {
+            assertEquals(json, Json.encodeToString(serializer, localTime))
+            assertEquals(localTime, Json.decodeFromString(serializer, json))
+        }
+    }
+
+    private fun defaultSerialization(serializer: KSerializer<LocalTime>) {
         for ((localTime, json) in listOf(
             Pair(LocalTime(2, 1), "\"02:01\""),
             Pair(LocalTime(23, 59, 1), "\"23:59:01\""),
@@ -59,17 +73,39 @@ class LocalTimeSerializationTest {
 
     @Test
     fun testIso8601Serialization() {
+        assertKSerializerName("kotlinx.datetime.LocalTime ISO", LocalTimeIso8601Serializer)
         iso8601Serialization(LocalTimeIso8601Serializer)
     }
 
     @Test
     fun testComponentSerialization() {
+        assertKSerializerName("kotlinx.datetime.LocalTime components", LocalTimeComponentSerializer)
         componentSerialization(LocalTimeComponentSerializer)
     }
 
     @Test
     fun testDefaultSerializers() {
-        // should be the same as the ISO 8601
-        iso8601Serialization(Json.serializersModule.serializer())
+        assertKSerializerName<LocalTime>("kotlinx.datetime.LocalTime", Json.serializersModule.serializer())
+        defaultSerialization(Json.serializersModule.serializer())
+    }
+
+    object FixedWidthTimeSerializer : FormattedLocalTimeSerializer("FixedWidth", LocalTime.Format {
+        hour(); char(':'); minute(); char(':'); second(); char('.'); secondFraction(3)
+    })
+
+    @Test
+    fun testCustomSerializer() {
+        assertKSerializerName("kotlinx.datetime.LocalTime serializer FixedWidth", FixedWidthTimeSerializer)
+        for ((localTime, json) in listOf(
+            Pair(LocalTime(2, 1), "\"02:01:00.000\""),
+            Pair(LocalTime(23, 59, 1), "\"23:59:01.000\""),
+            Pair(LocalTime(23, 59, 59, 990000000), "\"23:59:59.990\""),
+            Pair(LocalTime(23, 59, 59, 999000000), "\"23:59:59.999\""),
+        )) {
+            assertEquals(json, Json.encodeToString(FixedWidthTimeSerializer, localTime))
+            assertEquals(localTime, Json.decodeFromString(FixedWidthTimeSerializer, json))
+        }
+        assertEquals("\"12:34:56.123\"", Json.encodeToString(FixedWidthTimeSerializer,
+            LocalTime(12, 34, 56, 123999999)))
     }
 }
diff --git a/serialization/common/test/MonthSerializationTest.kt b/serialization/common/test/MonthSerializationTest.kt
index 3296ba08..70d9b455 100644
--- a/serialization/common/test/MonthSerializationTest.kt
+++ b/serialization/common/test/MonthSerializationTest.kt
@@ -13,10 +13,11 @@ import kotlin.test.*
 class MonthSerializationTest {
     @Test
     fun testSerialization() {
+        assertKSerializerName("kotlinx.datetime.Month", MonthSerializer)
         for (month in Month.entries) {
             val json = "\"${month.name}\""
             assertEquals(json, Json.encodeToString(MonthSerializer, month))
             assertEquals(month, Json.decodeFromString(MonthSerializer, json))
         }
     }
-}
\ No newline at end of file
+}
diff --git a/serialization/common/test/TimeZoneSerializationTest.kt b/serialization/common/test/TimeZoneSerializationTest.kt
index f4062b0b..b34f5633 100644
--- a/serialization/common/test/TimeZoneSerializationTest.kt
+++ b/serialization/common/test/TimeZoneSerializationTest.kt
@@ -46,7 +46,11 @@ class TimeZoneSerializationTest {
 
     @Test
     fun testDefaultSerializers() {
+        assertKSerializerName<FixedOffsetTimeZone>(
+            "kotlinx.datetime.FixedOffsetTimeZone", Json.serializersModule.serializer()
+        )
         zoneOffsetSerialization(Json.serializersModule.serializer())
+        assertKSerializerName<TimeZone>("kotlinx.datetime.TimeZone", Json.serializersModule.serializer())
         serialization(Json.serializersModule.serializer())
     }
-}
\ No newline at end of file
+}
diff --git a/serialization/common/test/UtcOffsetSerializationTest.kt b/serialization/common/test/UtcOffsetSerializationTest.kt
index 2504d6fb..b4ac0477 100644
--- a/serialization/common/test/UtcOffsetSerializationTest.kt
+++ b/serialization/common/test/UtcOffsetSerializationTest.kt
@@ -14,25 +14,66 @@ import kotlin.test.*
 
 class UtcOffsetSerializationTest {
 
-    private fun testSerializationAsPrimitive(serializer: KSerializer<UtcOffset>) {
-        val offset2h = UtcOffset(hours = 2)
-        assertEquals("\"+02:00\"", Json.encodeToString(serializer, offset2h))
-        assertEquals(offset2h, Json.decodeFromString(serializer, "\"+02:00\""))
-        assertEquals(offset2h, Json.decodeFromString(serializer, "\"+02:00:00\""))
-
-        assertFailsWith<IllegalArgumentException> {
-            Json.decodeFromString(serializer, "\"UTC+02:00\"") // not an offset
+    private fun iso8601Serialization(serializer: KSerializer<UtcOffset>) {
+        // the default form is obtainable and parsable
+        for ((offset, json) in listOf(
+            Pair(UtcOffset(hours = 0), "\"Z\""),
+            Pair(UtcOffset(hours = 1), "\"+01:00\""),
+            Pair(UtcOffset(hours = 1, minutes = 30), "\"+01:30\""),
+            Pair(UtcOffset(hours = 1, minutes = 30, seconds = 59), "\"+01:30:59\""),
+        )) {
+            assertEquals(json, Json.encodeToString(serializer, offset))
+            assertEquals(offset, Json.decodeFromString(serializer, json))
+        }
+        // alternative forms are also parsable
+        for ((offset, json) in listOf(
+            Pair(UtcOffset(hours = 0), "\"+00:00\""),
+            Pair(UtcOffset(hours = 0), "\"z\""),
+        )) {
+            assertEquals(offset, Json.decodeFromString(serializer, json))
+        }
+        // some strings aren't parsable
+        for (json in listOf(
+            "\"+3\"",
+            "\"+03\"",
+            "\"+03:0\"",
+            "\"UTC+02:00\"",
+        )) {
+            assertFailsWith<IllegalArgumentException> {
+                Json.decodeFromString(serializer, json)
+            }
         }
     }
 
     @Test
-    fun defaultSerializer() {
-        testSerializationAsPrimitive(Json.serializersModule.serializer())
+    fun testIso8601Serialization() {
+        assertKSerializerName<UtcOffset>("kotlinx.datetime.UtcOffset ISO", UtcOffsetIso8601Serializer)
+        iso8601Serialization(UtcOffsetIso8601Serializer)
     }
 
     @Test
-    fun stringPrimitiveSerializer() {
-        testSerializationAsPrimitive(UtcOffsetSerializer)
-        testSerializationAsPrimitive(UtcOffset.serializer())
+    fun testDefaultSerializers() {
+        // should be the same as the ISO 8601
+        assertKSerializerName<UtcOffset>("kotlinx.datetime.UtcOffset", Json.serializersModule.serializer())
+        iso8601Serialization(Json.serializersModule.serializer())
+        assertKSerializerName<UtcOffset>("kotlinx.datetime.UtcOffset", UtcOffset.serializer())
+        iso8601Serialization(UtcOffset.serializer())
+    }
+
+    object FourDigitOffsetSerializer : FormattedUtcOffsetSerializer("FOUR_DIGITS", UtcOffset.Formats.FOUR_DIGITS)
+
+    @Test
+    fun testCustomSerializer() {
+        assertKSerializerName("kotlinx.datetime.UtcOffset serializer FOUR_DIGITS", FourDigitOffsetSerializer)
+        for ((utcOffset, json) in listOf(
+            Pair(UtcOffset.ZERO, "\"+0000\""),
+            Pair(UtcOffset(2), "\"+0200\""),
+            Pair(UtcOffset(2, 30), "\"+0230\""),
+            Pair(UtcOffset(-2, -30), "\"-0230\""),
+        )) {
+            assertEquals(json, Json.encodeToString(FourDigitOffsetSerializer, utcOffset))
+            assertEquals(utcOffset, Json.decodeFromString(FourDigitOffsetSerializer, json))
+        }
+        assertEquals("\"+1234\"", Json.encodeToString(FourDigitOffsetSerializer, UtcOffset(12, 34, 56)))
     }
 }