petebacondarwin · Oct 13, 2026 · Oct 12, 2026
@@ -0,0 +1,9 @@
+---
+"wrangler": minor
+---
+
+Upload source maps by default for `wrangler deploy`, `wrangler versions upload` and `wrangler preview`
+
+When `upload_source_maps` isn't set in config or via `--upload-source-maps`, Wrangler now generates and uploads source maps so stack traces in logs and `wrangler tail` point at your original source without extra setup. In this default mode, source maps that can't be resolved (for example inline `data:` maps or missing `.map` files from a custom build) are skipped rather than failing the upload. Setting `upload_source_maps = true` keeps the existing strict behaviour, and `upload_source_maps = false` (or `--no-upload-source-maps` for deploy and versions upload) opts out.
+
+`wrangler build --experimental-cf-build-output` is unchanged and still only includes source maps when `upload_source_maps = true`.
@@ -830,6 +830,11 @@ interface EnvironmentInheritable {
 	/**
 	 * Include source maps when uploading this worker.
 	 *
+	 * Defaults to `true` for `wrangler deploy`, `wrangler versions upload` and
+	 * `wrangler preview`, where source maps that can't be resolved are skipped
+	 * rather than failing the upload. Defaults to `false` for
+	 * `wrangler build --experimental-cf-build-output`.
+	 *
 	 * For reference, see https://developers.cloudflare.com/workers/wrangler/configuration/#source-maps
 	 *
 	 * @inheritable

@@ -1350,6 +1350,62 @@ export default { fetch() { return new Response(mod); } };`;
 			await runWrangler("deploy");
 		});
 
+		it("should include source map with bundle by default", async ({
+			expect,
+		}) => {
+			writeWranglerConfig({ main: "index.ts" });
+			writeWorkerSource({ format: "ts" });
+			mockSubDomainRequest();
+			mockUploadWorkerRequest({
+				expectedMainModule: "index.js",
+				expectedModules: {
+					"index.js.map": expect.stringMatching(
+						/"sources":\["another.ts","index.ts"\],"sourceRoot":"".*"file":"index.js"/
+					),
+				},
+			});
+
+			await runWrangler("deploy");
+		});
+
+		it("should skip unresolvable source maps by default rather than failing", async () => {
+			writeWranglerConfig({ no_bundle: true, main: "index.js" });
+			fs.writeFileSync(
+				"index.js",
+				`export default { fetch() { return new Response("Hello World"); } }\n` +
+					"//# sourceMappingURL=missing.js.map"
+			);
+
+			mockSubDomainRequest();
+			mockUploadWorkerRequest({
+				expectedMainModule: "index.js",
+				expectedModules: {
+					"index.js.map": null,
+				},
+			});
+
+			await runWrangler("deploy");
+		});
+
+		it("should fail on unresolvable source maps when upload_source_maps = true", async ({
+			expect,
+		}) => {
+			writeWranglerConfig({
+				no_bundle: true,
+				main: "index.js",
+				upload_source_maps: true,
+			});
+			fs.writeFileSync(
+				"index.js",
+				`export default { fetch() { return new Response("Hello World"); } }\n` +
+					"//# sourceMappingURL=missing.js.map"
+			);
+
+			await expect(runWrangler("deploy")).rejects.toThrow(
+				/Invalid source map path in .*index\.js: .*missing\.js\.map does not exist\./
+			);
+		});
+
 		it("should not include source map with bundle when upload_source_maps = false", async () => {
 			writeWranglerConfig({
 				main: "index.ts",

@@ -1166,6 +1166,11 @@ export default{
 				Content-Type: application/wasm
 
 				Hello wasm World!
+				------formdata-undici-0.test
+				Content-Disposition: form-data; name="index.js.map"; filename="index.js.map"
+				Content-Type: application/source-map
+
+				{"version":3,"sources":["index.js"],"sourceRoot":"","sourcesContent":["\\nimport txt from './textfile.txt';\\nimport hello from './hello.wasm';\\nexport default{\\n  async fetch(){\\n\\t\\tconst module = await WebAssembly.instantiate(hello);\\n    return new Response(txt + module.exports.hello);\\n  }\\n}\\n"],"mappings":";AACA,OAAO,SAAS;AAChB,OAAO,WAAW;AAClB,IAAO,gBAAO;AAAA,EACZ,MAAM,QAAO;AACb,UAAM,SAAS,MAAM,YAAY,YAAY,KAAK;AAChD,WAAO,IAAI,SAAS,MAAM,OAAO,QAAQ,KAAK;AAAA,EAChD;AACF;","names":[],"file":"index.js"}
 				------formdata-undici-0.test--
 				"
 			`);
@@ -1311,6 +1316,11 @@ export default{
 				Content-Type: application/wasm
 
 				Hello wasm World!
+				------formdata-undici-0.test
+				Content-Disposition: form-data; name="index.js.map"; filename="index.js.map"
+				Content-Type: application/source-map
+
+				{"version":3,"sources":["index.js"],"sourceRoot":"","sourcesContent":["\\nimport txt from './textfile.txt';\\nimport hello from './hello.wasm';\\nexport default{\\n  async fetch(){\\n\\t\\tconst module = await WebAssembly.instantiate(hello);\\n    return new Response(txt + module.exports.hello);\\n  }\\n}\\n"],"mappings":";AACA,OAAO,SAAS;AAChB,OAAO,WAAW;AAClB,IAAO,gBAAO;AAAA,EACZ,MAAM,QAAO;AACb,UAAM,SAAS,MAAM,YAAY,YAAY,KAAK;AAChD,WAAO,IAAI,SAAS,MAAM,OAAO,QAAQ,KAAK;AAAA,EAChD;AACF;","names":[],"file":"index.js"}
 				------formdata-undici-0.test--
 				"
 			`);

@@ -51,6 +51,29 @@ describe("loadSourceMaps", () => {
 		expect(result[0].name).toBe("src/index.ts.map");
 	});
 
+	it("loads bundled source maps when the output path is absolute", ({
+		expect,
+	}) => {
+		const entryDir = createTempDir();
+		const outDir = createTempDir();
+		writeFileSync(path.join(outDir, "index.js.map"), validSourceMap);
+
+		const main = makeModule(
+			"index.js",
+			path.join(entryDir, "index.js"),
+			"const x = 1;\n"
+		);
+		const bundle: SourceMapBundle = {
+			sourceMapPath: path.join(outDir, "index.js.map"),
+			sourceMapMetadata: { tmpDir: outDir, entryDirectory: entryDir },
+		};
+
+		const result = loadSourceMaps(main, [], bundle);
+
+		expect(result).toHaveLength(1);
+		expect(result[0].name).toBe("index.js.map");
+	});
+
 	it("throws when bundled source map file is missing", ({ expect }) => {
 		const dir = createTempDir();
 		const main = makeModule(
@@ -85,6 +108,30 @@ describe("loadSourceMaps", () => {
 		expect(result[0].name).toBe("index.js.map");
 	});
 
+	it("skips unresolvable source maps in scan mode when not strict", ({
+		expect,
+	}) => {
+		const dir = createTempDir();
+		writeFileSync(path.join(dir, "other.js.map"), validSourceMap);
+
+		const main = makeModule(
+			"index.js",
+			path.join(dir, "index.js"),
+			`console.log("hello");\n//# sourceMappingURL=missing.js.map`
+		);
+		const other = makeModule(
+			"other.js",
+			path.join(dir, "other.js"),
+			`console.log("other");\n//# sourceMappingURL=other.js.map`
+		);
+
+		expect(() => loadSourceMaps(main, [other], {})).toThrow();
+
+		const result = loadSourceMaps(main, [other], {}, { strict: false });
+
+		expect(result.map((sourceMap) => sourceMap.name)).toEqual(["other.js.map"]);
+	});
+
 	it("handles multiple modules with source maps in scan mode", ({ expect }) => {
 		const dir = createTempDir();
 		writeFileSync(path.join(dir, "a.js.map"), validSourceMap);

@@ -6140,93 +6140,97 @@ describe("wrangler preview", () => {
 			);
 		});
 
-		test("should include source maps in deployment modules when upload_source_maps is enabled", async ({
-			expect,
-		}) => {
-			writeFileSync(
-				"wrangler.json",
-				JSON.stringify({
-					name: "test-worker",
-					main: "src/index.ts",
-					compatibility_date: "2025-01-01",
-					upload_source_maps: true,
-					previews: {},
-				})
-			);
+		test.for([
+			{ label: "enabled", uploadSourceMaps: true },
+			{ label: "unset", uploadSourceMaps: undefined },
+		])(
+			"should include source maps in deployment modules when upload_source_maps is $label",
+			async ({ uploadSourceMaps }, { expect }) => {
+				writeFileSync(
+					"wrangler.json",
+					JSON.stringify({
+						name: "test-worker",
+						main: "src/index.ts",
+						compatibility_date: "2025-01-01",
+						upload_source_maps: uploadSourceMaps,
+						previews: {},
+					})
+				);
 
-			let deploymentRequestBody:
-				| (Record<string, unknown> & {
-						modules?: PreviewDeploymentModulePart[];
-				  })
-				| undefined;
+				let deploymentRequestBody:
+					| (Record<string, unknown> & {
+							modules?: PreviewDeploymentModulePart[];
+					  })
+					| undefined;
 
-			msw.use(
-				http.get(
-					`*/accounts/:accountId/workers/workers/:workerId/previews/:previewId`,
-					() =>
-						HttpResponse.json(
-							{
-								success: false,
-								result: null,
-								errors: [{ code: 10025, message: "Preview not found" }],
-							},
-							{ status: 404 }
-						)
-				),
-				http.post(
-					`*/accounts/:accountId/workers/workers/:workerId/previews`,
-					() =>
-						HttpResponse.json(
-							{
-								success: true,
-								result: {
-									id: "preview-id-sourcemaps",
-									name: "test-preview",
-									slug: "test-preview",
-									urls: ["https://test-preview.test-worker.cloudflare.app"],
-									worker_name: "test-worker",
-									created_on: new Date().toISOString(),
+				msw.use(
+					http.get(
+						`*/accounts/:accountId/workers/workers/:workerId/previews/:previewId`,
+						() =>
+							HttpResponse.json(
+								{
+									success: false,
+									result: null,
+									errors: [{ code: 10025, message: "Preview not found" }],
 								},
-							},
-							{ status: 201 }
-						)
-				),
-				http.post(
-					`*/accounts/:accountId/workers/workers/:workerId/previews/:previewId/deployments`,
-					async ({ request }) => {
-						deploymentRequestBody = (await readPreviewDeploymentRequest(
-							request
-						)) as typeof deploymentRequestBody;
-						return HttpResponse.json(
-							{
-								success: true,
-								result: {
-									id: "deployment-id-sourcemaps",
-									preview_id: "preview-id-sourcemaps",
-									preview_name: "test-preview",
-									urls: ["https://sourcemaps123.test-worker.cloudflare.app"],
-									compatibility_date: "2025-01-01",
-									env: {},
-									created_on: new Date().toISOString(),
+								{ status: 404 }
+							)
+					),
+					http.post(
+						`*/accounts/:accountId/workers/workers/:workerId/previews`,
+						() =>
+							HttpResponse.json(
+								{
+									success: true,
+									result: {
+										id: "preview-id-sourcemaps",
+										name: "test-preview",
+										slug: "test-preview",
+										urls: ["https://test-preview.test-worker.cloudflare.app"],
+										worker_name: "test-worker",
+										created_on: new Date().toISOString(),
+									},
 								},
-							},
-							{ status: 201 }
-						);
-					}
-				)
-			);
+								{ status: 201 }
+							)
+					),
+					http.post(
+						`*/accounts/:accountId/workers/workers/:workerId/previews/:previewId/deployments`,
+						async ({ request }) => {
+							deploymentRequestBody = (await readPreviewDeploymentRequest(
+								request
+							)) as typeof deploymentRequestBody;
+							return HttpResponse.json(
+								{
+									success: true,
+									result: {
+										id: "deployment-id-sourcemaps",
+										preview_id: "preview-id-sourcemaps",
+										preview_name: "test-preview",
+										urls: ["https://sourcemaps123.test-worker.cloudflare.app"],
+										compatibility_date: "2025-01-01",
+										env: {},
+										created_on: new Date().toISOString(),
+									},
+								},
+								{ status: 201 }
+							);
+						}
+					)
+				);
 
-			await runWrangler("preview --name test-preview");
+				await runWrangler("preview --name test-preview");
 
-			const sourceMap = deploymentRequestBody?.modules?.find((module) =>
-				module.name.endsWith(".map")
-			);
+				const sourceMap = deploymentRequestBody?.modules?.find((module) =>
+					module.name.endsWith(".map")
+				);
 
-			expect(sourceMap?.content_type).toBe("application/source-map");
-			expect(JSON.parse(decodeModuleContent(sourceMap))).toEqual(
-				expect.objectContaining({ version: 3 })
-			);
-		});
+				expect(sourceMap?.content_type).toBe("application/source-map");
+				expect(JSON.parse(decodeModuleContent(sourceMap))).toEqual(
+					expect.objectContaining({ version: 3 })
+				);
+			}
+		);
 
 		test("should use previews.define for worker bundling", async ({
 			expect,

@@ -80,7 +80,7 @@ async function writeBundle({
 	}
 
 	// Source maps. `buildResult.sourceMaps` is already gated by
-	// `uploadSourceMaps` inside `buildWorker` (undefined when off) and
+	// `uploadSourceMaps` inside `buildWorker` (undefined when explicitly off) and
 	// contains the main module's map plus any module maps, each named
 	// `<module>.map` (e.g. `index.js.map`).
 	for (const sourceMap of buildResult.sourceMaps ?? []) {

@@ -143,7 +143,8 @@ export const sharedDeployVersionsArgs = {
 		type: "boolean",
 	},
 	"upload-source-maps": {
-		describe: "Include source maps when uploading this Worker",
+		describe:
+			"Include source maps when uploading this Worker (defaults to true)",
 		type: "boolean",
 	},
 	"node-compat": {