diff --git a/.dockerignore b/.dockerignore
index a7fb9a9..744faae 100644
--- a/.dockerignore
+++ b/.dockerignore
@@ -2,7 +2,6 @@ node_modules
 **/node_modules
 **/dist
 **/*.tsbuildinfo
-.git
 .tools
 data
 data-dev
diff --git a/Dockerfile b/Dockerfile
index 48b06c7..02e8317 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,6 +1,7 @@
 # ---- Stage 1: build shared + client (static assets) ----
 FROM node:20-bookworm-slim AS build-client
 WORKDIR /app
+RUN apt-get update && apt-get install -y --no-install-recommends git && rm -rf /var/lib/apt/lists/*
 COPY package.json ./
 COPY shared/package.json shared/package.json
 COPY server/package.json server/package.json
@@ -8,11 +9,13 @@ COPY client/package.json client/package.json
 RUN npm install
 COPY shared shared
 COPY client client
+COPY .git .git
 RUN npm run build -w shared && npm run build -w client
 
 # ---- Stage 2: build shared + server (compiled JS) ----
 FROM node:20-bookworm-slim AS build-server
 WORKDIR /app
+RUN apt-get update && apt-get install -y --no-install-recommends git && rm -rf /var/lib/apt/lists/*
 COPY package.json ./
 COPY shared/package.json shared/package.json
 COPY server/package.json server/package.json
@@ -20,6 +23,7 @@ COPY client/package.json client/package.json
 RUN npm install
 COPY shared shared
 COPY server server
+COPY .git .git
 RUN npm run build -w shared && npm run build -w server
 
 # ---- Stage 3: runtime ----
diff --git a/client/src/api/version.ts b/client/src/api/version.ts
new file mode 100644
index 0000000..c61c889
--- /dev/null
+++ b/client/src/api/version.ts
@@ -0,0 +1,6 @@
+import type { AppVersion } from '@citytracker/shared';
+import { api } from './client';
+
+export function fetchVersion() {
+  return api.get<AppVersion>('/version');
+}
diff --git a/client/src/components/layout/AppShell.tsx b/client/src/components/layout/AppShell.tsx
index c73c46e..884d657 100644
--- a/client/src/components/layout/AppShell.tsx
+++ b/client/src/components/layout/AppShell.tsx
@@ -1,5 +1,6 @@
 import { NavLink, Outlet, useNavigate } from 'react-router-dom';
 import { useAuth } from '../../context/AuthContext';
+import { AppVersion } from './AppVersion';
 
 export function AppShell() {
   const { user, logout } = useAuth();
@@ -14,6 +15,7 @@ export function AppShell() {
     <div className="app-shell">
       <header className="app-header">
         <span className="app-title">CityTracker</span>
+        <AppVersion />
         <nav className="app-nav">
           <NavLink to="/" end>
             Map
diff --git a/client/src/components/layout/AppVersion.tsx b/client/src/components/layout/AppVersion.tsx
new file mode 100644
index 0000000..c9690ef
--- /dev/null
+++ b/client/src/components/layout/AppVersion.tsx
@@ -0,0 +1,31 @@
+import { useEffect, useState } from 'react';
+import type { AppVersion as AppVersionInfo } from '@citytracker/shared';
+import { fetchVersion } from '../../api/version';
+
+const clientVersion = __APP_VERSION__;
+
+export function AppVersion() {
+  const [serverVersion, setServerVersion] = useState<AppVersionInfo | null>(null);
+
+  useEffect(() => {
+    fetchVersion()
+      .then(setServerVersion)
+      .catch(() => undefined);
+  }, []);
+
+  const stale = serverVersion !== null && serverVersion.commit !== clientVersion.commit;
+
+  const title = [
+    `Loaded build: ${clientVersion.commit} (${clientVersion.builtAt})`,
+    serverVersion
+      ? `Server build: ${serverVersion.commit} (${serverVersion.builtAt})`
+      : 'Server build: checking…',
+  ].join('\n');
+
+  return (
+    <span className={`app-version${stale ? ' app-version-stale' : ''}`} title={title}>
+      {clientVersion.commit}
+      {stale && ' — reload for latest'}
+    </span>
+  );
+}
diff --git a/client/src/styles/global.css b/client/src/styles/global.css
index 7a2d727..3904176 100644
--- a/client/src/styles/global.css
+++ b/client/src/styles/global.css
@@ -135,6 +135,16 @@ a {
   font-size: 1.1rem;
 }
 
+.app-version {
+  font-size: 0.75rem;
+  color: var(--color-text-muted);
+  font-family: monospace;
+}
+
+.app-version-stale {
+  color: var(--color-primary);
+}
+
 .app-nav {
   display: flex;
   gap: var(--spacing-3);
diff --git a/client/src/vite-env.d.ts b/client/src/vite-env.d.ts
index ec878b7..1e246ff 100644
--- a/client/src/vite-env.d.ts
+++ b/client/src/vite-env.d.ts
@@ -1,2 +1,4 @@
 /// <reference types="vite/client" />
 /// <reference types="vite-plugin-pwa/react" />
+
+declare const __APP_VERSION__: { commit: string; builtAt: string };
diff --git a/client/vite.config.ts b/client/vite.config.ts
index 55c08f5..6b554e0 100644
--- a/client/vite.config.ts
+++ b/client/vite.config.ts
@@ -1,8 +1,20 @@
+import { execSync } from 'node:child_process';
 import { defineConfig } from 'vite';
 import react from '@vitejs/plugin-react';
 import { VitePWA } from 'vite-plugin-pwa';
 
+function getCommit(): string {
+  try {
+    return execSync('git rev-parse --short HEAD').toString().trim();
+  } catch {
+    return 'dev';
+  }
+}
+
 export default defineConfig({
+  define: {
+    __APP_VERSION__: JSON.stringify({ commit: getCommit(), builtAt: new Date().toISOString() }),
+  },
   plugins: [
     react(),
     VitePWA({
diff --git a/server/package.json b/server/package.json
index 03daf1c..943d04c 100644
--- a/server/package.json
+++ b/server/package.json
@@ -5,7 +5,7 @@
   "main": "dist/index.js",
   "scripts": {
     "dev": "tsx watch src/index.ts",
-    "build": "tsc && node -e \"require('fs').cpSync('src/db/migrations','dist/db/migrations',{recursive:true})\"",
+    "build": "tsc && node -e \"require('fs').cpSync('src/db/migrations','dist/db/migrations',{recursive:true})\" && node scripts/write-version.js",
     "start": "node dist/index.js",
     "clean": "rimraf dist"
   },
diff --git a/server/scripts/write-version.js b/server/scripts/write-version.js
new file mode 100644
index 0000000..e4a2797
--- /dev/null
+++ b/server/scripts/write-version.js
@@ -0,0 +1,20 @@
+const { execSync } = require('node:child_process');
+const fs = require('node:fs');
+const path = require('node:path');
+
+function getCommit() {
+  try {
+    return execSync('git rev-parse --short HEAD', { cwd: __dirname }).toString().trim();
+  } catch {
+    return 'dev';
+  }
+}
+
+const version = {
+  commit: getCommit(),
+  builtAt: new Date().toISOString(),
+};
+
+const outDir = path.join(__dirname, '..', 'dist');
+fs.mkdirSync(outDir, { recursive: true });
+fs.writeFileSync(path.join(outDir, 'version.json'), JSON.stringify(version));
diff --git a/server/src/app.ts b/server/src/app.ts
index 41231e7..a6fa52b 100644
--- a/server/src/app.ts
+++ b/server/src/app.ts
@@ -15,6 +15,8 @@ export function createApp() {
   app.use(express.json());
   app.use(sessionMiddleware);
 
+  app.get('/api/version', (req, res) => res.json(config.version));
+
   app.use('/api/auth', authRouter);
   app.use('/api/users', usersRouter);
   app.use('/api/cities', citiesRouter);
diff --git a/server/src/config.ts b/server/src/config.ts
index b2a0c78..bfb4b20 100644
--- a/server/src/config.ts
+++ b/server/src/config.ts
@@ -1,11 +1,32 @@
 import path from 'node:path';
 import crypto from 'node:crypto';
+import fs from 'node:fs';
+import { execSync } from 'node:child_process';
+import type { AppVersion } from '@citytracker/shared';
 
 function readBool(value: string | undefined, fallback: boolean): boolean {
   if (value === undefined) return fallback;
   return value.toLowerCase() === 'true' || value === '1';
 }
 
+// In the Docker image this file is written at build time by scripts/write-version.js and
+// sits next to this compiled file in dist/. Under `tsx` in local dev there's no build step,
+// so fall back to asking git directly for the current commit.
+function readVersion(): AppVersion {
+  try {
+    const raw = fs.readFileSync(path.join(__dirname, 'version.json'), 'utf-8');
+    return JSON.parse(raw) as AppVersion;
+  } catch {
+    let commit = 'dev';
+    try {
+      commit = execSync('git rev-parse --short HEAD', { cwd: __dirname }).toString().trim();
+    } catch {
+      // no .git available either (e.g. a source-only deploy) — leave commit as 'dev'
+    }
+    return { commit, builtAt: new Date().toISOString() };
+  }
+}
+
 const isProduction = process.env.NODE_ENV === 'production';
 
 let sessionSecret = process.env.SESSION_SECRET;
@@ -34,4 +55,5 @@ export const config = {
   // file's location, not process.cwd(), since cwd depends on how the process was launched.
   clientDistDir:
     process.env.CLIENT_DIST_DIR || path.join(__dirname, '..', '..', 'client', 'dist'),
+  version: readVersion(),
 };
diff --git a/shared/src/types.ts b/shared/src/types.ts
index f02c562..ca8b280 100644
--- a/shared/src/types.ts
+++ b/shared/src/types.ts
@@ -47,3 +47,8 @@ export interface GeocodeResult {
 export interface SetupStatus {
   needsSetup: boolean;
 }
+
+export interface AppVersion {
+  commit: string;
+  builtAt: string;
+}