diff --git a/internal/receipt/markdown.go b/internal/receipt/markdown.go
index f18a7ca..81884bb 100644
--- a/internal/receipt/markdown.go
+++ b/internal/receipt/markdown.go
@@ -91,7 +91,7 @@ func WriteMarkdown(w io.Writer, r schema.Receipt) {
 	if cov.SuppressedMentions > 0 {
 		fmt.Fprintf(w, "<sub>%s</sub>\n", mentionNote(cov.SuppressedMentions))
 	}
-	fmt.Fprintf(w, "\n<sub>schema %s · exit gate: refuted claims block; the remainder informs, never fails</sub>\n", r.SchemaVersion)
+	fmt.Fprintf(w, "\n<sub>schema %s%s · exit gate: refuted claims block; the remainder informs, never fails</sub>\n", r.SchemaVersion, toolNote(r))
 }
 
 // mdCell makes text safe inside a markdown table cell.
diff --git a/internal/receipt/receipt.go b/internal/receipt/receipt.go
index 729e5ae..4bb83f8 100644
--- a/internal/receipt/receipt.go
+++ b/internal/receipt/receipt.go
@@ -11,7 +11,9 @@ import (
 	"path"
 	"path/filepath"
 	"regexp"
+	"runtime/debug"
 	"strings"
+	"sync"
 
 	"github.com/joshft/correctful/internal/gitdiff"
 	"github.com/joshft/correctful/schema"
@@ -59,6 +61,7 @@ func Assemble(change gitdiff.Change, claims []schema.Claim, evidence [][]schema.
 
 	return schema.Receipt{
 		SchemaVersion: schema.SchemaVersion,
+		ToolVersion:   toolVersion(),
 		Change: schema.ChangeRef{
 			// The receipt carries the repository NAME, never its location: a
 			// receipt is shareable, and external-tool details are scrubbed of
@@ -86,6 +89,45 @@ func Assemble(change gitdiff.Change, claims []schema.Claim, evidence [][]schema.
 	}
 }
 
+// toolVersion identifies this checker build from its own build info — the
+// first chain field: two receipts are comparable across time only when the
+// harvesters and runners that produced them are known. Module version plus
+// short VCS revision when the build is stamped (`go install` from a clone
+// stamps both; a dirty tree gains "+dirty"), "unknown" when the build
+// carries no identity — stated, never guessed.
+var toolVersion = sync.OnceValue(func() string {
+	bi, ok := debug.ReadBuildInfo()
+	if !ok {
+		return "unknown"
+	}
+	v := bi.Main.Version
+	rev, dirty := "", false
+	for _, s := range bi.Settings {
+		switch s.Key {
+		case "vcs.revision":
+			rev = s.Value
+		case "vcs.modified":
+			dirty = s.Value == "true"
+		}
+	}
+	if len(rev) > 12 {
+		rev = rev[:12]
+	}
+	if rev != "" && dirty {
+		rev += "+dirty"
+	}
+	switch {
+	case v != "" && rev != "":
+		return v + " " + rev
+	case v != "":
+		return v
+	case rev != "":
+		return rev
+	default:
+		return "unknown"
+	}
+})
+
 // anchoringSummary tallies the binding layer's resolution outcomes. Nil when
 // no claim carries an anchor — a repo without a definition corpus.
 func anchoringSummary(claims []schema.Claim) *schema.AnchoringSummary {
@@ -350,7 +392,7 @@ func WriteJSON(w io.Writer, r schema.Receipt) error {
 // every other tool hides.
 func WriteText(w io.Writer, r schema.Receipt) {
 	s := r.Summary
-	fmt.Fprintf(w, "correctful receipt (schema %s)\n", r.SchemaVersion)
+	fmt.Fprintf(w, "correctful receipt (schema %s%s)\n", r.SchemaVersion, toolNote(r))
 	fmt.Fprintf(w, "change: %s...%s%s", r.Change.BaseRef, r.Change.HeadRef, shaNote(r.Change))
 	if r.Change.Repo != "" {
 		fmt.Fprintf(w, "  [%s]", r.Change.Repo)
@@ -438,6 +480,15 @@ func mentionNote(n int) string {
 	return fmt.Sprintf("%d spec-id mention(s) not minted as claims — the repo defines no spec-id corpus, so a reference has no possible referent", n)
 }
 
+// toolNote renders the producing build beside the schema version — shared by
+// both renderers so the chain field is visible wherever the receipt is read.
+func toolNote(r schema.Receipt) string {
+	if r.ToolVersion == "" {
+		return ""
+	}
+	return " · correctful " + r.ToolVersion
+}
+
 // detailOf picks the evidence detail a reader needs: for a refuted claim, the
 // FAILING probe's detail — a claim with five probes where the fourth failed
 // must not display the first probe's "ok".
diff --git a/internal/receipt/receipt_test.go b/internal/receipt/receipt_test.go
index 661ec69..1eef2f8 100644
--- a/internal/receipt/receipt_test.go
+++ b/internal/receipt/receipt_test.go
@@ -492,3 +492,24 @@ func TestLLMVerifiedRowKeepsProvenance(t *testing.T) {
 		}
 	}
 }
+
+// TestReceiptCarriesToolVersion: the first chain field. Every receipt names
+// the build that produced it — "unknown" when the build carries no identity,
+// never empty — and both renderers show it beside the schema version.
+func TestReceiptCarriesToolVersion(t *testing.T) {
+	claims, evidence := sampleClaims()
+	r := Assemble(gitdiff.Change{BaseRef: "main", HeadRef: "wip"}, claims, evidence, schema.Coverage{})
+	if r.ToolVersion == "" {
+		t.Fatal("tool version empty — must be stated, or stated as unknown")
+	}
+	var text, md strings.Builder
+	WriteText(&text, r)
+	WriteMarkdown(&md, r)
+	want := "correctful " + r.ToolVersion
+	if !strings.Contains(text.String(), want) {
+		t.Errorf("text receipt lacks %q", want)
+	}
+	if !strings.Contains(md.String(), want) {
+		t.Errorf("markdown receipt lacks %q", want)
+	}
+}
diff --git a/schema/schema.go b/schema/schema.go
index 771a3e1..4df49a8 100644
--- a/schema/schema.go
+++ b/schema/schema.go
@@ -374,9 +374,17 @@ type Coverage struct {
 // Receipt is the per-change output: what was claimed, what was verified, and —
 // the load-bearing part — the honest unverified remainder.
 type Receipt struct {
-	SchemaVersion string        `json:"schema_version"`
-	Change        ChangeRef     `json:"change"`
-	Results       []ClaimResult `json:"results"`
+	SchemaVersion string `json:"schema_version"`
+	// ToolVersion identifies the checker build that produced this receipt —
+	// module version plus VCS revision when the build carries them, so two
+	// receipts are comparable across time only when the harvesters and
+	// runners that produced them are known. One field covers every in-tree
+	// component (they ship in one binary); per-supplier versions arrive with
+	// the evidence-intake contract. "unknown" when the build carries no
+	// identity — stated, never guessed.
+	ToolVersion string        `json:"tool_version,omitempty"`
+	Change      ChangeRef     `json:"change"`
+	Results     []ClaimResult `json:"results"`
 	// Remainder is the subset of Results with Status == StatusUnverified,
 	// surfaced explicitly so a reader never has to derive it. This is the
 	// feature no other tool in the field ships.
@@ -386,4 +394,4 @@ type Receipt struct {
 }
 
 // SchemaVersion is the current version of the receipt schema (the payload).
-const SchemaVersion = "0.0.9"
+const SchemaVersion = "0.0.10"