diff --git a/src/cache/lock.ts b/src/cache/lock.ts
index 4e5f262..c42c69b 100644
--- a/src/cache/lock.ts
+++ b/src/cache/lock.ts
@@ -9,12 +9,10 @@ export interface DocsCacheLockSource {
 	fileCount: number;
 	manifestSha256: string;
 	rulesSha256?: string;
-	updatedAt: string;
 }
 
 export interface DocsCacheLock {
 	version: 1;
-	generatedAt: string;
 	toolVersion: string;
 	sources: Record<string, DocsCacheLockSource>;
 }
@@ -54,7 +52,6 @@ export const validateLock = (input: unknown): DocsCacheLock => {
 	if (version !== 1) {
 		throw new Error("Lock file version must be 1.");
 	}
-	const generatedAt = assertString(input.generatedAt, "generatedAt");
 	const toolVersion = assertString(input.toolVersion, "toolVersion");
 	if (!isRecord(input.sources)) {
 		throw new Error("sources must be an object.");
@@ -84,12 +81,10 @@ export const validateLock = (input: unknown): DocsCacheLock => {
 				value.rulesSha256 === undefined
 					? undefined
 					: assertString(value.rulesSha256, `sources.${key}.rulesSha256`),
-			updatedAt: assertString(value.updatedAt, `sources.${key}.updatedAt`),
 		};
 	}
 	return {
 		version: 1,
-		generatedAt,
 		toolVersion,
 		sources,
 	};
diff --git a/src/commands/sync.ts b/src/commands/sync.ts
index 018d368..064d02d 100644
--- a/src/commands/sync.ts
+++ b/src/commands/sync.ts
@@ -221,7 +221,6 @@ const loadToolVersion = async () => {
 const buildLockSource = (
 	result: SyncResult,
 	prior: DocsCacheLock["sources"][string] | undefined,
-	now: string,
 ) => ({
 	repo: result.repo,
 	ref: result.ref,
@@ -231,7 +230,6 @@ const buildLockSource = (
 	manifestSha256:
 		result.manifestSha256 ?? prior?.manifestSha256 ?? result.resolvedCommit,
 	rulesSha256: result.rulesSha256 ?? prior?.rulesSha256,
-	updatedAt: now,
 });
 
 const buildLock = async (
@@ -239,7 +237,6 @@ const buildLock = async (
 	previous: Awaited<ReturnType<typeof readLock>> | null,
 ) => {
 	const toolVersion = await loadToolVersion();
-	const now = new Date().toISOString();
 	const configSourceIds = new Set(
 		plan.config.sources.map((source) => source.id),
 	);
@@ -253,11 +250,10 @@ const buildLock = async (
 	}
 	for (const result of plan.results) {
 		const prior = sources[result.id];
-		sources[result.id] = buildLockSource(result, prior, now);
+		sources[result.id] = buildLockSource(result, prior);
 	}
 	return {
 		version: 1 as const,
-		generatedAt: now,
 		toolVersion,
 		sources,
 	};
diff --git a/tests/edge-cases.test.js b/tests/edge-cases.test.js
index b64520a..1d7a210 100644
--- a/tests/edge-cases.test.js
+++ b/tests/edge-cases.test.js
@@ -222,7 +222,6 @@ test("lock file with invalid version", async () => {
 
 	const invalidLock = {
 		version: 2,
-		generatedAt: new Date().toISOString(),
 		toolVersion: "0.1.0",
 		sources: {},
 	};
@@ -249,7 +248,7 @@ test("lock file with missing required fields", async () => {
 
 	const invalidLock = {
 		version: 1,
-		// missing generatedAt, toolVersion, sources
+		// missing toolVersion, sources
 	};
 	await writeFile(lockPath, JSON.stringify(invalidLock, null, 2), "utf8");
 
@@ -259,7 +258,7 @@ test("lock file with missing required fields", async () => {
 	} = await import("node:fs/promises");
 	const raw = await read(lockPath, "utf8");
 	const parsed = JSON.parse(raw);
-	assert.equal(parsed.generatedAt, undefined);
+	assert.equal(parsed.toolVersion, undefined);
 });
 
 test("lock file with negative bytes", async () => {
@@ -272,7 +271,6 @@ test("lock file with negative bytes", async () => {
 
 	const invalidLock = {
 		version: 1,
-		generatedAt: new Date().toISOString(),
 		toolVersion: "0.1.0",
 		sources: {
 			test: {
@@ -282,7 +280,6 @@ test("lock file with negative bytes", async () => {
 				bytes: -100,
 				fileCount: 5,
 				manifestSha256: "def456",
-				updatedAt: new Date().toISOString(),
 			},
 		},
 	};
diff --git a/tests/fixtures/docs-lock.json b/tests/fixtures/docs-lock.json
index c45932c..d4910a9 100644
--- a/tests/fixtures/docs-lock.json
+++ b/tests/fixtures/docs-lock.json
@@ -1,6 +1,5 @@
 {
 	"version": 1,
-	"generatedAt": "2026-01-30T12:00:00+01:00",
 	"toolVersion": "0.1.0",
 	"sources": {
 		"vitest": {
@@ -10,8 +9,7 @@
 			"bytes": 123456,
 			"fileCount": 512,
 			"manifestSha256": "abcd",
-			"rulesSha256": "efgh",
-			"updatedAt": "2026-01-30T12:00:00+01:00"
+			"rulesSha256": "efgh"
 		}
 	}
 }
diff --git a/tests/fixtures/empty.docs-lock.json b/tests/fixtures/empty.docs-lock.json
index e2c5d66..427341b 100644
--- a/tests/fixtures/empty.docs-lock.json
+++ b/tests/fixtures/empty.docs-lock.json
@@ -1,6 +1,5 @@
 {
 	"version": 1,
-	"generatedAt": "2026-01-30T12:00:00+01:00",
 	"toolVersion": "0.1.0",
 	"sources": {}
 }
diff --git a/tests/lock.test.js b/tests/lock.test.js
index fff11b1..2ed45fe 100644
--- a/tests/lock.test.js
+++ b/tests/lock.test.js
@@ -42,11 +42,10 @@ test("writeLock produces readable JSON", async (t) => {
 	const tmpPath = path.join(tmpdir(), `docs-lock-${Date.now()}.json`);
 	const lock = {
 		version: 1,
-		generatedAt: "2026-01-30T12:00:00+01:00",
 		toolVersion: "0.1.0",
 		sources: {},
 	};
 	await module.writeLock(tmpPath, lock);
 	const parsed = await module.readLock(tmpPath);
-	assert.equal(parsed.generatedAt, lock.generatedAt);
+	assert.deepEqual(parsed, lock);
 });
diff --git a/tests/sync-materialize.test.js b/tests/sync-materialize.test.js
index 99f7d31..da53c7b 100644
--- a/tests/sync-materialize.test.js
+++ b/tests/sync-materialize.test.js
@@ -230,7 +230,6 @@ test("sync re-materializes when docs missing even if commit unchanged", async ()
 		path.join(tmpRoot, DEFAULT_LOCK_FILENAME),
 		JSON.stringify({
 			version: 1,
-			generatedAt: new Date().toISOString(),
 			toolVersion: "0.1.0",
 			sources: {
 				local: {
@@ -240,7 +239,6 @@ test("sync re-materializes when docs missing even if commit unchanged", async ()
 					bytes: 0,
 					fileCount: 0,
 					manifestSha256: "abc123",
-					updatedAt: new Date().toISOString(),
 				},
 			},
 		}),
@@ -315,7 +313,6 @@ test("sync offline materializes from cache when lock exists", async () => {
 		path.join(tmpRoot, DEFAULT_LOCK_FILENAME),
 		JSON.stringify({
 			version: 1,
-			generatedAt: new Date().toISOString(),
 			toolVersion: "0.1.0",
 			sources: {
 				local: {
@@ -325,7 +322,6 @@ test("sync offline materializes from cache when lock exists", async () => {
 					bytes: 0,
 					fileCount: 0,
 					manifestSha256: "abc123",
-					updatedAt: new Date().toISOString(),
 				},
 			},
 		}),
diff --git a/tests/sync-offline-fail.test.js b/tests/sync-offline-fail.test.js
index d662ce7..296b4e5 100644
--- a/tests/sync-offline-fail.test.js
+++ b/tests/sync-offline-fail.test.js
@@ -75,7 +75,6 @@ test("sync offline uses lock entries without resolving remotes", async () => {
 		lockPath,
 		JSON.stringify({
 			version: 1,
-			generatedAt: new Date().toISOString(),
 			toolVersion: "0.1.0",
 			sources: {
 				local: {
@@ -85,7 +84,6 @@ test("sync offline uses lock entries without resolving remotes", async () => {
 					bytes: 4,
 					fileCount: 1,
 					manifestSha256: "abc123",
-					updatedAt: new Date().toISOString(),
 				},
 			},
 		}),
@@ -145,7 +143,6 @@ test("sync offline fails when lock exists but cache missing", async () => {
 		lockPath,
 		JSON.stringify({
 			version: 1,
-			generatedAt: new Date().toISOString(),
 			toolVersion: "0.1.0",
 			sources: {
 				local: {
@@ -155,7 +152,6 @@ test("sync offline fails when lock exists but cache missing", async () => {
 					bytes: 4,
 					fileCount: 1,
 					manifestSha256: "abc123",
-					updatedAt: new Date().toISOString(),
 				},
 			},
 		}),