diff --git a/gdf.js b/gdf.js
index 4f6eb87..a97255e 100755
--- a/gdf.js
+++ b/gdf.js
@@ -50,6 +50,12 @@ const ALPINE_MAPPINGS = {
 const __dirname = url.fileURLToPath(new URL('.', import.meta.url))
 
 // Generate Dockerfile class
+const BUN_SCRIPT_EXTENSIONS = ['.ts', '.tsx', '.mts', '.cts', '.js', '.jsx', '.mjs', '.cjs']
+
+// bun flags that take a separate value, e.g. --preload ./instrument.ts
+const BUN_VALUE_FLAGS = ['--preload', '-r', '--require', '--import', '--config', '-c', '--cwd',
+  '--env-file', '--tsconfig-override', '--define', '-d', '--loader', '-l', '--conditions']
+
 export class GDF {
   static templates = path.join(__dirname, 'templates')
   static runners = []
@@ -836,6 +842,119 @@ export class GDF {
     return this.bun ? 'bunx' : 'npx'
   }
 
+  // Is filename an existing script file in the app directory?
+  bunScript(filename) {
+    if (!BUN_SCRIPT_EXTENSIONS.includes(path.posix.extname(filename))) return false
+    return !!fs.statSync(path.join(this._appdir, filename), { throwIfNoEntry: false })?.isFile()
+  }
+
+  // The TypeScript source of a missing foo.js, if there is one
+  bunSource(entry) {
+    if (fs.existsSync(path.join(this._appdir, entry))) return entry
+    const extension = path.posix.extname(entry)
+    const base = extension ? entry.slice(0, -extension.length) : entry
+    const sources = extension === '.cjs' ? ['.cts'] : ['.ts', '.tsx', '.mts']
+    return sources.map(ext => base + ext).find(file => this.bunScript(file)) || entry
+  }
+
+  // Could a script produce a declared entry point that doesn't exist yet?
+  get bunBuildsEntry() {
+    const { build, prepare, postinstall } = this.#pj.scripts || {}
+    return !!(build || prepare || postinstall)
+  }
+
+  // A declared foo.js may be missing because only foo.ts exists.  Bun 1.2+
+  // runs foo.ts in that case, older versions fail, so point at the source,
+  // unless foo.js could be build output.
+  bunEntry(entry) {
+    return this.bunBuildsEntry ? entry : this.bunSource(entry)
+  }
+
+  // The directory and file run by the last `bun` command in the dev script,
+  // e.g. src/server.ts in "bun run codegen.ts && bun --watch src/server.ts",
+  // or apps/api and src/index.ts in "cd apps/api && bun --watch src/index.ts"
+  get bunDevEntry() {
+    const devScript = this.#pj.scripts?.dev
+    if (!devScript) return null
+
+    let entry = null
+    let command // the current command, null once its file is found
+    let skip = false // the next token is a flag value or redirect target
+    let dir = '.' // null when the directory can't be followed
+    let listDir = dir // directory at the start of the current command list
+    const dirs = [] // directories outside of (subshells)
+
+    for (const token of ShellQuote.parse(devScript)) {
+      if (typeof token !== 'string') {
+        if (token.comment !== undefined) continue
+        if (token.op === 'glob') {
+          if (command === 'bun') command = null
+          continue
+        }
+        if (/^\d*[<>]/.test(token.op)) {
+          skip = true
+          continue
+        }
+
+        // a bare cd changes to $HOME
+        if (command === 'cd') dir = null
+
+        if (token.op === '(') {
+          dirs.push(dir)
+        } else if (token.op === ')') {
+          dir = dirs.length ? dirs.pop() : null
+        } else if (token.op === '&' || token.op === '|') {
+          // background lists and pipelines run in subshells
+          dir = listDir
+        }
+
+        if (token.op === ';' || token.op === '&') listDir = dir
+        command = undefined
+        skip = false
+      } else if (skip) {
+        skip = false
+      } else if (command === undefined) {
+        if (!/^\w+=/.test(token)) command = token
+      } else if (command === 'cd') {
+        // only follow relative directories that stay within the app
+        const target = dir === null || path.posix.isAbsolute(token) || /^[~-]/.test(token)
+          ? null
+          : path.posix.normalize(path.posix.join(dir, token)).replace(/\/+$/, '') || '.'
+        dir = target === null || target === '..' || target.startsWith('../') ? null : target
+        command = null
+      } else if (command === 'bun') {
+        if (token.startsWith('-')) {
+          skip = BUN_VALUE_FLAGS.includes(token)
+        } else if (token !== 'run') {
+          // the first file is the entry; anything after it is its argv
+          const file = dir === null ? null : this.bunSource(path.posix.join(dir, token))
+          if (file && this.bunScript(file)) entry = { dir, file: path.posix.relative(dir, file) }
+          command = null
+        }
+      }
+    }
+
+    return entry
+  }
+
+  // Bun apps without a start script, main, or module with type: module.
+  // An existing index.ts is what has always been used here, so it wins;
+  // otherwise look for the entry (e.g. src/index.ts in the Elysia template).
+  get bunStartCommand() {
+    if (this.bunScript('index.ts')) return ['bun', 'index.ts']
+
+    // a declared module that doesn't exist yet is likely build output
+    const module = this.#pj.module && this.bunEntry(this.#pj.module)
+    if (module && (this.bunScript(module) || this.bunBuildsEntry)) return ['bun', module]
+
+    // a dev script that changes directory names the app explicitly
+    const dev = this.bunDevEntry
+    if (dev && dev.dir !== '.') return ['bun', '--cwd', dev.dir, dev.file]
+    if (this.bunScript('src/index.ts')) return ['bun', 'src/index.ts']
+
+    return ['bun', dev?.file || module || 'index.ts']
+  }
+
   // command to start the web server
   get startCommand() {
     if (this.options.cmd) return this.options.cmd
@@ -883,13 +1002,13 @@ export class GDF {
     } else if (this.#pj.scripts?.start) {
       return [this.packager, 'run', 'start']
     } else if (this.#pj.type === 'module' && this.#pj.module) {
-      return [this.packager === 'bun' ? 'bun' : 'node', this.#pj.module]
+      return this.packager === 'bun' ? ['bun', this.bunEntry(this.#pj.module)] : ['node', this.#pj.module]
     } else if (this.#pj.main) {
-      return [this.packager === 'bun' ? 'bun' : 'node', this.#pj.main]
+      return this.packager === 'bun' ? ['bun', this.bunEntry(this.#pj.main)] : ['node', this.#pj.main]
     } else if (this.svelte) {
       return [this.bun ? 'bun' : 'node', './build/index.js']
     } else if (this.packager === 'bun') {
-      return ['bun', 'index.ts']
+      return this.bunStartCommand
     } else {
       return ['node', 'index.js']
     }
diff --git a/test/gdf.test.js b/test/gdf.test.js
index fe074c5..b736c13 100644
--- a/test/gdf.test.js
+++ b/test/gdf.test.js
@@ -656,6 +656,7 @@ describe('gdf: start command and port', function() {
   it('uses bun for module, main and the default entry point', async function() {
     sandbox().stub('bun', 'echo 1.1.20\n')
     sandbox().write('bun.lockb', '')
+    sandbox().write('app.ts', '')
 
     let gdf = await sandbox().run({ main: 'app.ts' })
     expect(gdf.startCommand).to.deep.equal(['bun', 'app.ts'])
@@ -664,6 +665,237 @@ describe('gdf: start command and port', function() {
     expect(gdf.startCommand).to.deep.equal(['bun', 'index.ts'])
   })
 
+  it('resolves a Bun module entry point to its TypeScript file when type is unspecified', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/index.ts', '')
+
+    const gdf = await sandbox().run({ module: 'src/index.js' })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'src/index.ts'])
+  })
+
+  it('keeps a Bun main entry point that has not been built yet', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/index.ts', '')
+
+    const gdf = await sandbox().run({ main: 'dist/index.js' })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'dist/index.js'])
+  })
+
+  it('keeps an existing Bun index.ts over module and dev script entries', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('index.ts', '')
+    sandbox().write('lib/index.js', '')
+    sandbox().write('src/app.css', '')
+
+    let gdf = await sandbox().run({ module: 'lib/index.js' })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'index.ts'])
+
+    gdf = await sandbox().run({ module: 'dist/index.mjs' })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'index.ts'])
+
+    gdf = await sandbox().run({ scripts: { dev: 'bun --watch index.ts & bunx tailwindcss -i src/app.css' } })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'index.ts'])
+  })
+
+  it('skips Bun dev script arguments that are not script files', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/server.ts', '')
+    sandbox().write('src/app.css', '')
+    sandbox().write('prisma/schema.prisma', '')
+
+    let gdf = await sandbox().run({ scripts: { dev: 'bun --watch src/server.ts --port $PORT' } })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'src/server.ts'])
+
+    gdf = await sandbox().run({ scripts: { dev: 'bun --watch src/server.ts & bunx tailwindcss -i src/app.css & bunx prisma studio' } })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'src/server.ts'])
+  })
+
+  it('keeps a Bun main entry point that is compiled from TypeScript', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('index.ts', '')
+
+    const gdf = await sandbox().run({ main: 'index.js', scripts: { build: 'tsc' } })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'index.js'])
+  })
+
+  it('uses the file run by the last bun command in the dev script', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/server.ts', '')
+    sandbox().write('scripts/codegen.ts', '')
+    sandbox().write('drizzle.config.ts', '')
+    sandbox().write('instrument.ts', '')
+
+    for (const dev of [
+      'bun run scripts/codegen.ts && bun --watch src/server.ts',
+      'bunx drizzle-kit push --config drizzle.config.ts && bun --watch src/server.ts',
+      'bun --preload ./instrument.ts src/server.ts',
+      'NODE_ENV=development bun --watch src/server.ts'
+    ]) {
+      const gdf = await sandbox().run({ scripts: { dev } })
+      expect(gdf.startCommand, dev).to.deep.equal(['bun', 'src/server.ts'])
+    }
+  })
+
+  it('runs a Bun dev entry point in the directory the dev script changes to', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/index.ts', '')
+    sandbox().write('apps/api/src/index.ts', '')
+
+    let gdf = await sandbox().run({ scripts: { dev: 'cd apps/api && bun --watch src/index.ts' } })
+    expect(gdf.startCommand).to.deep.equal(['bun', '--cwd', 'apps/api', 'src/index.ts'])
+
+    gdf = await sandbox().run({ scripts: { dev: 'cd apps && cd api && bun --watch ./src/index.js' } })
+    expect(gdf.startCommand).to.deep.equal(['bun', '--cwd', 'apps/api', 'src/index.ts'])
+
+    expect(sandbox().read('Dockerfile')).to.include('CMD [ "bun", "--cwd", "apps/api", "src/index.ts" ]')
+  })
+
+  it('treats arguments after the Bun dev entry point as its argv', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/server.ts', '')
+    sandbox().write('drizzle.config.ts', '')
+
+    for (const dev of [
+      'bun --watch src/server.ts --config drizzle.config.ts',
+      'bun --watch src/server.ts > log.txt 2>&1',
+      'bun --watch src/server.ts # drizzle.config.ts'
+    ]) {
+      const gdf = await sandbox().run({ scripts: { dev } })
+      expect(gdf.startCommand, dev).to.deep.equal(['bun', 'src/server.ts'])
+    }
+  })
+
+  it('does not follow cd out of Bun dev script subshells and background jobs', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('server.ts', '')
+    sandbox().write('web/server.ts', '')
+
+    for (const dev of [
+      '(cd web && vite) & bun --watch server.ts',
+      'cd web && vite & bun --watch server.ts',
+      'cd ./ && bun --watch server.ts'
+    ]) {
+      const gdf = await sandbox().run({ scripts: { dev } })
+      expect(gdf.startCommand, dev).to.deep.equal(['bun', 'server.ts'])
+    }
+
+    const gdf = await sandbox().run({ scripts: { dev: 'cd web/ && bun --watch server.ts' } })
+    expect(gdf.startCommand).to.deep.equal(['bun', '--cwd', 'web', 'server.ts'])
+  })
+
+  it('resolves a missing Bun main or module to its TypeScript source unless a script builds it', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/index.ts', '')
+    sandbox().write('src/worker.cts', '')
+
+    let gdf = await sandbox().run({ type: 'module', module: 'src/index.js' })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'src/index.ts'])
+
+    gdf = await sandbox().run({ main: 'src/worker.cjs' })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'src/worker.cts'])
+
+    gdf = await sandbox().run({ type: 'module', module: 'src/index.js', scripts: { build: 'tsc' } })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'src/index.js'])
+
+    gdf = await sandbox().run({ main: 'src/index.js', scripts: { prepare: 'tsc' } })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'src/index.js'])
+  })
+
+  it('prefers a Bun module built by a script over the dev script entry point', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/server.ts', '')
+
+    const gdf = await sandbox().run({
+      module: 'dist/index.mjs',
+      scripts: { build: 'bun build src/server.ts --outdir dist', dev: 'bun --watch src/server.ts' }
+    })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'dist/index.mjs'])
+  })
+
+  it('ignores Bun dev script entry points outside the app', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/index.ts', '')
+
+    for (const dev of ['cd .. && bun --watch src/index.ts', 'cd /srv && bun src/index.ts', 'cd ~ && bun src/index.ts', 'cd && bun src/index.ts']) {
+      const gdf = await sandbox().run({ scripts: { dev } })
+      expect(gdf.startCommand, dev).to.deep.equal(['bun', 'src/index.ts'])
+    }
+  })
+
+  it('prefers a Bun src/index.ts over the dev script entry point', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/index.ts', '')
+    sandbox().write('src/dev.ts', '')
+
+    const gdf = await sandbox().run({ scripts: { dev: 'bun --watch src/dev.ts' } })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'src/index.ts'])
+  })
+
+  it('resolves a Bun module entry point to its TSX file', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/index.tsx', '')
+
+    const gdf = await sandbox().run({ module: 'src/index.js' })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'src/index.tsx'])
+  })
+
+  it('keeps a Bun module entry point that has not been built yet', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+
+    const gdf = await sandbox().run({ module: 'dist/index.mjs' })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'dist/index.mjs'])
+  })
+
+  it('skips a Bun module entry point that does not exist', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/server.ts', '')
+
+    const gdf = await sandbox().run({ module: 'dist/index.mjs', scripts: { dev: 'bun --watch src/server.ts' } })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'src/server.ts'])
+  })
+
+  it('uses the Bun dev entry point without --watch', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/server.ts', '')
+
+    const gdf = await sandbox().run({ scripts: { dev: 'bun --watch src/server.ts' } })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'src/server.ts'])
+  })
+
+  it('runs a Bun start script when one is defined', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+
+    const gdf = await sandbox().run({ scripts: { start: 'bun src/server.ts' } })
+    expect(gdf.startCommand).to.deep.equal(['bun', 'run', 'start'])
+  })
+
+  it('uses src/index.ts when a Bun project has no module or dev entry point', async function() {
+    sandbox().stub('bun', 'echo 1.1.20\n')
+    sandbox().write('bun.lockb', '')
+    sandbox().write('src/index.ts', '')
+
+    const gdf = await sandbox().run({})
+    expect(gdf.startCommand).to.deep.equal(['bun', 'src/index.ts'])
+  })
+
   it('starts standalone next.js with server.js', async function() {
     for (const config of ['next.config.js', 'next.config.mjs']) {
       fs.rmSync('next.config.js', { force: true })