diff --git a/apps/micropolis/cli/wasm/sim.ts b/apps/micropolis/cli/wasm/sim.ts
index c4d8b09c..f080b0a7 100644
--- a/apps/micropolis/cli/wasm/sim.ts
+++ b/apps/micropolis/cli/wasm/sim.ts
@@ -4,13 +4,14 @@
  * `extendSimCommands(argv)` adds the `sim` branch using the shared WASM loader.
  */
 
+import { writeFileSync } from 'node:fs';
 import type { Argv } from 'yargs';
 import type { MainModule, Micropolis } from '../../src/types/micropolisengine.d.js';
 import { createNoopJsCallback } from '../../src/lib/wasm/callbacks';
 import { loadMicropolisMainModule } from '../../src/lib/wasm/node';
 import { normalizeStructuredFormat, stringifyStructured } from '../lib/format.js';
 
-type Flags = { city?: string; ticks?: number; format?: string };
+type Flags = { city?: string; ticks?: number; format?: string; output?: string };
 
 function stringFlag(v: unknown, fallback: string): string {
 	return typeof v === 'string' && v.length > 0 ? v : fallback;
@@ -53,6 +54,7 @@ function summarize(
 async function runSmoke(flags: Flags) {
 	const ticks = numberFlag(flags.ticks, 10);
 	const city = stringFlag(flags.city, '/cities/haight.cty');
+	const output = stringFlag(flags.output, '');
 	const engine = await loadMicropolisMainModule();
 	const micropolis = new engine.Micropolis();
 	const cb = createNoopJsCallback(engine);
@@ -61,7 +63,18 @@ async function runSmoke(flags: Flags) {
 	try {
 		const loaded = micropolis.loadCity(city);
 		for (let i = 0; i < ticks; i += 1) micropolis.simTick();
-		return summarize(engine, micropolis, { loaded, city, ticks });
+		const summary = summarize(engine, micropolis, { loaded, city, ticks });
+		let saved: string | null = null;
+		let bytes = 0;
+		if (output.length > 0) {
+			const savedPath = '/micropolis-save.cty';
+			micropolis.saveCityAs(savedPath);
+			const buf = engine.FS_readFile(savedPath) as Uint8Array;
+			writeFileSync(output, buf);
+			saved = output;
+			bytes = buf.length;
+		}
+		return { ...summary, saved, bytes };
 	} finally {
 		micropolis.delete();
 	}
@@ -104,6 +117,11 @@ export function extendSimCommands(argv: Argv): Argv {
 							describe: 'Virtual path passed to loadCity (packaged .cty)'
 						})
 						.option('ticks', { type: 'number', default: 10, describe: 'Number of simTick() calls' })
+						.option('output', {
+							alias: 'o',
+							type: 'string',
+							describe: 'Write the city to this .cty file after ticking'
+						})
 						.option('format', {
 							alias: 'f',
 							type: 'string',
diff --git a/apps/micropolis/src/types/micropolisengine.d.ts b/apps/micropolis/src/types/micropolisengine.d.ts
index cba61954..fb969107 100644
--- a/apps/micropolis/src/types/micropolisengine.d.ts
+++ b/apps/micropolis/src/types/micropolisengine.d.ts
@@ -1,5 +1,6 @@
 // TypeScript bindings for emscripten-generated code.  Automatically generated at compile time.
 declare namespace RuntimeExports {
+    function FS_readFile(...args: any[]): any;
     let HEAPU16: Uint16Array;
     let wasmMemory: any;
     function FS_createPath(...args: any[]): any;
@@ -369,6 +370,7 @@ export interface Micropolis extends ClassHandle {
   setCallback(_0: Callback | null, _1: any): void;
   init(): void;
   loadCity(_0: EmbindString): boolean;
+  saveCityAs(_0: EmbindString): void;
   simTick(): void;
   simUpdate(): void;
   generateSomeRandomCity(): void;
diff --git a/packages/micropolis-engine/makefile b/packages/micropolis-engine/makefile
index 7655a936..241f957b 100644
--- a/packages/micropolis-engine/makefile
+++ b/packages/micropolis-engine/makefile
@@ -78,7 +78,7 @@ EMLDFLAGS = \
     -s EXPORT_ES6=1 \
     -s 'ENVIRONMENT=web,worker,node' \
     -s ALLOW_MEMORY_GROWTH=1 \
-    -s 'EXPORTED_RUNTIME_METHODS=["HEAPU16","wasmMemory"]' \
+    -s 'EXPORTED_RUNTIME_METHODS=["FS_readFile","HEAPU16","wasmMemory"]' \
 	-lembind \
 	--emit-tsd=micropolisengine.d.ts \
 	--shell-file src/micropolisengine_template.html \
diff --git a/packages/micropolis-engine/src/emscripten.cpp b/packages/micropolis-engine/src/emscripten.cpp
index 303229cd..afe9383c 100644
--- a/packages/micropolis-engine/src/emscripten.cpp
+++ b/packages/micropolis-engine/src/emscripten.cpp
@@ -1076,6 +1076,7 @@ function createTypedArrayFromMap(mapInstance) {
     .function("setCallback", &Micropolis::setCallback, allow_raw_pointers())
     .function("init", &Micropolis::init)
     .function("loadCity", &Micropolis::loadCity)
+    .function("saveCityAs", &Micropolis::saveCityAs)
     .function("simTick", &Micropolis::simTick)
     .function("simUpdate", &Micropolis::simUpdate)
     .function("generateSomeRandomCity", &Micropolis::generateSomeRandomCity)