diff --git a/cmd/qrank-builder/itemsignals.go b/cmd/qrank-builder/itemsignals.go
index 1057888..3dcb200 100644
--- a/cmd/qrank-builder/itemsignals.go
+++ b/cmd/qrank-builder/itemsignals.go
@@ -6,15 +6,108 @@ package main
 import (
 	"bytes"
 	"context"
+	"encoding/binary"
 	"fmt"
 	"os"
 	"regexp"
 	"time"
 
 	"github.com/klauspost/compress/zstd"
+	"github.com/lanrat/extsort"
 	"github.com/minio/minio-go/v7"
 )
 
+// ItemSignals contains ranking signals for Wikidata items.
+type ItemSignals struct {
+	item          int64 // eg 72 for Q72
+	pageviews     int64
+	wikitextBytes int64
+	claims        int64
+	identifiers   int64
+	sitelinks     int64
+}
+
+// If we ever want to rank signals for Wikidata lexemes, it would
+// probably make sense to use a separate struct (written to a different
+// output file) because it's likely not the same set of signals.
+// For example, lexemes don't have pageviews, pagerank or wikitextBytes.
+// https://github.com/brawer/wikidata-qrank/issues/37
+// type LexemeSignals struct {}
+
+func (s ItemSignals) ToBytes() []byte {
+	buf := make([]byte, binary.MaxVarintLen64*6)
+	p := binary.PutVarint(buf, s.item)
+	p += binary.PutVarint(buf[p:], s.pageviews)
+	p += binary.PutVarint(buf[p:], s.wikitextBytes)
+	p += binary.PutVarint(buf[p:], s.claims)
+	p += binary.PutVarint(buf[p:], s.identifiers)
+	p += binary.PutVarint(buf[p:], s.sitelinks)
+	return buf[0:p]
+}
+
+func ItemSignalsFromBytes(b []byte) extsort.SortType {
+	item, pos := binary.Varint(b)
+	pageviews, n := binary.Varint(b[pos:])
+	pos += n
+	wikitextBytes, n := binary.Varint(b[pos:])
+	pos += n
+	claims, n := binary.Varint(b[pos:])
+	pos += n
+	identifiers, n := binary.Varint(b[pos:])
+	pos += n
+	sitelinks, n := binary.Varint(b[pos:])
+	return ItemSignals{
+		item:          item,
+		pageviews:     pageviews,
+		wikitextBytes: wikitextBytes,
+		claims:        claims,
+		identifiers:   identifiers,
+		sitelinks:     sitelinks,
+	}
+}
+
+func ItemSignalsLess(a, b extsort.SortType) bool {
+	aa, bb := a.(ItemSignals), b.(ItemSignals)
+
+	if aa.item < bb.item {
+		return true
+	} else if aa.item > bb.item {
+		return false
+	}
+
+	if aa.pageviews < bb.pageviews {
+		return true
+	} else if aa.pageviews > bb.pageviews {
+		return false
+	}
+
+	if aa.wikitextBytes < bb.wikitextBytes {
+		return true
+	} else if aa.wikitextBytes > bb.wikitextBytes {
+		return false
+	}
+
+	if aa.claims < bb.claims {
+		return true
+	} else if aa.claims > bb.claims {
+		return false
+	}
+
+	if aa.identifiers < bb.identifiers {
+		return true
+	} else if aa.identifiers > bb.identifiers {
+		return false
+	}
+
+	if aa.sitelinks < bb.sitelinks {
+		return true
+	} else if aa.sitelinks > bb.sitelinks {
+		return false
+	}
+
+	return false
+}
+
 // BuildItemSignals builds per-item signals and puts them in storage.
 // If the signals file is already in storage, it does not get re-built.
 func buildItemSignals(ctx context.Context, pageviews []string, sites *map[string]WikiSite, s3 S3) (time.Time, error) {
diff --git a/cmd/qrank-builder/itemsignals_test.go b/cmd/qrank-builder/itemsignals_test.go
index 31fec91..32a0737 100644
--- a/cmd/qrank-builder/itemsignals_test.go
+++ b/cmd/qrank-builder/itemsignals_test.go
@@ -7,11 +7,68 @@ import (
 	"bytes"
 	"context"
 	"log"
+	"reflect"
 	"slices"
 	"testing"
 	"time"
 )
 
+func TestItemSignalsToBytes(t *testing.T) {
+	// Serialize and then de-serialize an ItemSignals struct.
+	a := ItemSignals{1, 2, 3, 4, 5, 6}
+	got := ItemSignalsFromBytes(a.ToBytes()).(ItemSignals)
+	if !reflect.DeepEqual(got, a) {
+		t.Errorf("got %v, want %v", got, a)
+	}
+}
+
+func TestItemSignalsLess(t *testing.T) {
+	for _, tc := range []struct {
+		a    string
+		b    string
+		want bool
+	}{
+		{"123456", "123456", false},
+		{"923456", "123456", false},
+		{"123456", "923456", true},
+
+		{"------", "------", false},
+		{"7-----", "------", false},
+		{"-7----", "------", false},
+		{"--7---", "------", false},
+		{"---7--", "------", false},
+		{"----7-", "------", false},
+		{"-----7", "------", false},
+		{"------", "7-----", true},
+		{"------", "-7----", true},
+		{"------", "--7---", true},
+		{"------", "---7--", true},
+		{"------", "----7-", true},
+		{"------", "-----7", true},
+	} {
+		a := ItemSignals{
+			item:          int64(tc.a[0]),
+			pageviews:     int64(tc.a[1]),
+			wikitextBytes: int64(tc.a[2]),
+			claims:        int64(tc.a[3]),
+			identifiers:   int64(tc.a[4]),
+			sitelinks:     int64(tc.a[5]),
+		}
+		b := ItemSignals{
+			item:          int64(tc.b[0]),
+			pageviews:     int64(tc.b[1]),
+			wikitextBytes: int64(tc.b[2]),
+			claims:        int64(tc.b[3]),
+			identifiers:   int64(tc.b[4]),
+			sitelinks:     int64(tc.b[5]),
+		}
+		got := ItemSignalsLess(a, b)
+		if got != tc.want {
+			t.Errorf("got %v, want %v, for ItemSignalsLess(%#v, %#v)", got, tc.want, a, b)
+		}
+	}
+}
+
 func TestBuildItemSignals(t *testing.T) {
 	logger = log.New(&bytes.Buffer{}, "", log.Lshortfile)
 	ctx := context.Background()