Browserbash

BrowserBash

Plain-English browser automation. No selectors. Free and open-source.

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[BrowserBash demo]

You write a plain-English objective. An AI agent drives a real Chrome browser step by step — no selectors, no scripts. Ollama-first, so it runs on free local models with no API keys and nothing ever leaves your machine.

npm install -g browserbash-clibrowserbash run "Open news.ycombinator.com and store the top story title as 'top_story'"

Website · Docs / Learn · Tutorials · npm

Both layers are swappable: the engine interprets the English, the provider runs the browser.

Engines (who interprets the English)

Providers (where the browser runs)

LLM backends (who does the thinking) — open source first

Default model is auto, resolved in this order:

1. Ollama running locally → ollama/<OLLAMA_MODEL or first installed model> — free, open source, no keys
2. ANTHROPIC_API_KEY set → claude-opus-4-8
3. OPENAI_API_KEY set → openai/gpt-4.1
4. otherwise: error with setup guidance

Fully free / open-source stack (the default)

ollama pull qwen3                 # or any tool-capable local modelbrowserbash run "Open https://example.com and store the heading as 'h1'"

Stagehand engine (MIT) + local Chromium + Ollama (MIT) — zero cloud cost, no API keys. Tip: small models (≤8B) are flaky on multi-step objectives; Qwen3 / Llama 3.3 70B class works best.

Note: cloud-grid providers (lambdatest, browserstack) use the builtin engine, which speaks the Anthropic API — pair them with ANTHROPIC_API_KEY or an ANTHROPIC_BASE_URL gateway.

Install

npm installnpm run buildnpm link        # exposes the `browserbash` command

Requires Node ≥ 18 and Google Chrome stable (for the local provider).

Quick start

export ANTHROPIC_API_KEY=sk-ant-...
# One-shot objective, local browser, Stagehand engine (default)browserbash run "Open https://news.ycombinator.com and store the top story title as 'top_story'"
# Browserbase cloud (Stagehand native)export BROWSERBASE_API_KEY=... BROWSERBASE_PROJECT_ID=...browserbash run "..." --provider browserbase
# Cloud grid (auto-switches to builtin engine)export LT_USERNAME=... LT_ACCESS_KEY=...browserbash run "..." --provider lambdatest --headless
# Attach to an existing browser (CDP / Playwright MCP)browserbash run "..." --cdp-endpoint ws://localhost:9222/devtools/browser/<id>
# Force the builtin enginebrowserbash run "..." --engine builtin

Agent mode (for AI coding tools & CI)

--agent switches stdout to NDJSON — one JSON object per line, stable schema:

browserbash run "<objective>" --agent --headless --timeout 120

• Progress events: {"type":"step","step":1,"status":"passed","action":"navigate","remark":"...","cached":false}
• Terminal event: {"type":"run_end","status":"passed|failed|error|timeout","summary":"...","final_state":{...},"duration_ms":...,"provider":"local","cache":"hit|miss|off","tokens_in":...,"tokens_out":...,"test_url":"..."}

Exit codes: 0 passed · 1 failed · 2 error · 3 timeout. cached, cache, tokens_in/tokens_out are additive fields (present when relevant), so existing consumers are unaffected.

Full agent integration guide: docs/agents.md.

MCP server (agents consume BrowserBash natively)

BrowserBash is a validation layer for AI agents: your coding agent builds a feature, BrowserBash proves it works in a real browser. One line plugs it into any MCP host:

claude mcp add browserbash -- browserbash mcp     # Claude Code# Cursor / Windsurf / Zed / Codex: command "browserbash", args ["mcp"]

Tools exposed: run_objective (one plain-English objective), run_test_file (a *_test.md), run_suite (a folder, parallel). Each returns the structured verdict JSON: status, summary, final_state, assertions, cost_usd, duration_ms. A failed test is a successful validation, so the tool call succeeds and the agent reads the verdict. No extra dependencies, stdio only, nothing leaves your machine.

Dashboards

Every run is kept in a private on-disk store (~/.browserbash/runs, secrets masked, capped at 200). Two ways to see them:

Local dashboard — free, no account, fully local:

browserbash dashboard                 # serve http://localhost:4477 and open itbrowserbash run "..." --record --dashboard   # run, then open the dashboard on this runbrowserbash dashboard --clear         # wipe the local store

Left panel lists your runs; the main pane shows the verdict, extracted values and the recording — with --record you get a screenshot plus a session video (stagehand engine, video needs ffmpeg, bundled) or a native Playwright trace you can open at trace.playwright.dev (builtin engine). Nothing leaves your machine.

Cloud dashboard — optional, opt-in per run: a hosted dashboard at browserbash.com/dashboard with run history across machines and shareable per-run pages.

browserbash connect --key bb_...      # one-time, key from browserbash.com/dashboardbrowserbash run "..." --record --upload   # push THIS run (verdict + recording) to the cloud

Without --upload nothing is sent to the cloud. BrowserBash is free and open source; cloud runs are kept 15 days.

Replay cache (warm runs skip the model)

A green run records the actions it took. The next identical run replays them with zero model calls, and the agent only steps back in when the page actually changed. Steady-state suites run at close to script speed and cost.

browserbash testmd run ./checkout_test.md            # run 1: records the journalbrowserbash testmd run ./checkout_test.md            # run 2: replays, no modelbrowserbash testmd run ./checkout_test.md --no-cache      # ignore the cache for this runbrowserbash testmd run ./checkout_test.md --refresh-cache # wipe this test's entry, re-record

run_end.cache reports hit / miss / off. On by default; config set cache.enabled false to disable, cache.dir to relocate (default .browserbash/cache, gitignored by init). Secrets never enter the cache: values arrive through the variables channel (Stagehand) or are re-templatized to {{name}} tokens (builtin), and any cached action that types a secret is origin-pinned — replaying it on a different origin fails closed. Builtin journals are also HMAC-signed with a per-machine key (~/.browserbash/cache.key); an edited or foreign journal is ignored and simply re-recorded. CI fleets that want to share committed caches can set the same BROWSERBASH_CACHE_KEY (64 hex chars) on every runner.

Parallel suites (run-all)

Run a whole folder of *_test.md files at once with memory-aware scheduling:

browserbash run-all .browserbash/tests --concurrency 8 --junit out/junit.xml

• Concurrency is auto-derived from CPU and free memory (min(requested, cpus, floor((mem - 2GB) / budget))), so big suites do not thrash the machine. Override with --concurrency, tune the estimate with --memory-budget <mb>. A hard watchdog also kills any test whose whole process tree (Node + Chromium) exceeds --memory-cap <mb> (default 2x the budget, 0 disables); the test is reported as an infra error with a test_kill event, and retried per --retries.
• Each test runs as an isolated child process with its own Result.md; a failure never leaks state to the next test.
• --retries <n> retries infra errors only (not real failures), --max-failures <n> stops early, --stagger <ms> softens burst load.
• Outputs: a merged NDJSON stream (--events, add --agent to also stream on stdout), JUnit XML (--junit), and a RunAll-Result.md with a flaky column.
• Run history in .browserbash/memory/history.json orders the next run (previously-failed first, then slowest first) and flags flaky tests. --no-memory opts out.
• Sharding: --shard 2/4 runs a deterministic slice, computed on sorted discovery order so parallel CI machines agree without coordination.
• Viewport matrix: --matrix-viewport 1280x720,390x844 runs every test once per viewport; cells are labeled in events, JUnit and results. Single runs take --viewport WxH too.
• Budgets: --budget-usd 2.50 (or --budget-tokens) stops launching new tests once estimated spend crosses the budget; the rest are reported skipped and the suite exits 2. Spend lands in RunAll-Result.md and JUnit <properties>.
• Webhooks: --notify <url> POSTs the suite verdict when it ends (Slack URLs get Slack formatting).
• Exit code: 0 all passed · 1 any failed · 2 infra error or budget stop · 3 suite timeout.

Cheap-model routing

Plan on a strong model, execute on a cheap one, escalate back automatically after a failed step:

browserbash run "..." --model claude-opus-4-8 --model-exec claude-haiku-4-5

run_end reports tokens_in / tokens_out (builtin engine) so you can see what a run costs, plus a cost_usd estimate from a bundled per-model price table (override at ~/.browserbash/pricing.json; unknown models get no estimate rather than a wrong one). Set persistently with config set routing.executionModel <id>.

Test files (*_test.md)

Committable, reviewable Markdown tests:

# Login flow
- Open {{base_url}}/login- Type {{username}} into the email field- Type {{password}} into the password field and press Enter- Verify the dashboard heading is visible- Store the logged-in user name as 'user_name'

browserbash testmd run ./.browserbash/tests/login_test.md --provider browserstack

Composition via @import ./helpers/login.md (steps are spliced in place). After every run a Result.md is written next to the test file.

testmd v2: assertions and API steps that never lie

Add version: 2 frontmatter and steps execute ONE AT A TIME against a single browser session, with two deterministic step types that never touch a model:

---version: 2auth: staging---# Checkout with seeded data
- POST {{base_url}}/api/seed with body {"sku": "tshirt-red"}- Expect status 201, store $.order.id as 'order_id'- Open {{base_url}}/cart- Click the checkout button- Verify the URL contains 'checkout'- Verify the 'Thank you for your order!' heading is visible- Verify stored 'order_id' equals '{{expected_id}}'

• API steps (GET/POST/PUT/DELETE/PATCH url [with body {...}] + Expect status N[, store $.path as 'name']) run as plain HTTP: seed data, then verify through the UI. Stored values feed {{variables}} in later steps.
• Verify steps compile to real Playwright checks (URL contains, title is/contains, text visible, 'name' button|link|heading visible, element counts, stored equals). A pass means the condition held; a fail comes with expected vs actual evidence in run_end.assertions and the Result.md assertion table. Verify lines outside the grammar still run, agent-judged and flagged judged: true.
• Consecutive plain-English steps run as grouped agent blocks on the same page, so login state and navigation carry through.
• v1 files (no frontmatter) behave exactly as before. v2 currently drives the builtin engine (needs ANTHROPIC_API_KEY or an ANTHROPIC_BASE_URL gateway).

Variables

{{key}} placeholders are substituted in objectives and test steps. Load order (highest priority last):

1. Global: ~/.browserbash/variables/*.json
2. Project: ./.browserbash/variables/*.json
3. --variables-file <path>
4. --variables '<json>'

Mark sensitive values {"value": "...", "secret": true} — they are masked as ***** in all logs and NDJSON output.

Saved logins (browserbash auth)

Real suites live behind a login. Log in once, reuse the session everywhere:

browserbash auth save staging --url https://app.example.com/login   # log in, press Enterbrowserbash run "Open the dashboard and store the balance as 'balance'" --auth stagingbrowserbash run-all .browserbash/tests --auth staging               # every test, no re-loginbrowserbash auth list && browserbash auth delete staging

Sessions are Playwright storageState files in ~/.browserbash/auth/ (mode 0600, they hold live credentials). Test files can pin their own profile with auth: staging frontmatter. A profile whose saved origins do not cover the target URL prints a warning instead of silently doing nothing.

Author tests without writing them

# Record: click through the flow once in a real browser, get a test filebrowserbash record https://app.example.com --out .browserbash/tests/checkout_test.md
# Import: convert an existing Playwright suite to plain Englishbrowserbash import ./e2e --out-dir .browserbash/imported

record captures clicks, typing and navigation (password values never leave the page; the generated step reads Type {{password}} into ...). import translates common Playwright calls deterministically and writes everything it could NOT translate to IMPORT-REPORT.md instead of guessing. Both outputs are starting points to review, not gospel.

Monitoring (browserbash monitor)

The same tests double as production checks:

browserbash monitor .browserbash/tests/checkout_test.md --every 10m \  --notify https://hooks.slack.com/services/T0/B0/xyz

Alerts fire on pass<->fail STATE CHANGES only, both directions, never on every green run. Slack webhook URLs get Slack formatting; any other URL receives the raw JSON payload. With the replay cache warm, a monitor makes zero model calls until the page actually changes.

Configuration

browserbash init                          # scaffold ./.browserbash/browserbash config showbrowserbash config set defaultProvider lambdatestbrowserbash providers                     # list providersbrowserbash login --provider lambdatest --username "$USER" --access-key "$KEY"browserbash whoami

Precedence: flags > env vars > ~/.browserbash/config.json defaults.

CI recipe (GitHub Actions)

- run: npm ci && npm run build- run: |    node dist/index.js login --provider lambdatest --username "$LT_USERNAME" --access-key "$LT_ACCESS_KEY"    node dist/index.js testmd run .browserbash/tests/smoke_test.md --agent --headless --timeout 180  env:    ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}    LT_USERNAME: ${{ secrets.LT_USERNAME }}    LT_ACCESS_KEY: ${{ secrets.LT_ACCESS_KEY }}

The process exit code is the test verdict — no output parsing needed.

Or use the official GitHub Action (PR verdict comment, artifacts, sharded matrix jobs, budget stop):

- uses: PramodDutta/browserbash@main  with:    tests: .browserbash/tests    budget-usd: '2.00'  env:    ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}

Full guide: docs/github-action.md.

Architecture

src/├── index.ts            # CLI (commander): run, testmd, run-all, monitor, auth, record, import, mcp, ...├── runner.ts           # engine routing + provider session + replay cache + vendor status reporting├── engine/│   ├── stagehand.ts    # default engine: Stagehand agent (stagehand.dev, MIT) — LOCAL / cdpUrl / Browserbase│   ├── agent.ts        # builtin engine: Anthropic tool-use loop (manual loop → NDJSON step events)│   ├── tools.ts        # builtin browser tools: navigate, snapshot, click, type_text, wait_for, extract, done│   ├── assertions.ts   # deterministic Verify grammar + executor (no model in the loop)│   ├── replay.ts       # builtin replay-first cache: replay recorded actions, origin-pinned│   └── routing.ts      # per-model thinking config + cheap-exec model routing├── providers/          # vendor abstraction — add a new vendor by implementing BrowserProvider│   ├── types.ts        # BrowserProvider / ProviderSession + context options (auth, viewport)│   ├── local.ts        # system Chrome│   ├── cdp.ts          # attach to any CDP endpoint (incl. Playwright MCP browsers)│   ├── lambdatest.ts   # LambdaTest/TestMu grid + setTestStatus reporting│   └── browserstack.ts # BrowserStack Automate grid + setSessionStatus reporting├── orchestrator/       # run-all: memory-aware scheduler + child-process suite runner│   ├── scheduler.ts    # concurrency formula, admission watermark, shard/matrix, JUnit│   └── run-all.ts      # spawn children, aggregate NDJSON, verdicts, retries, budgets├── mcp/server.ts       # MCP stdio server: run_objective / run_test_file / run_suite├── testmd/             # parser (@import, frontmatter), v1 runner, v2 per-step runner + API steps├── import/playwright.ts# heuristic Playwright spec -> *_test.md converter├── record/             # interactive recorder: capture script + events -> English steps├── monitor.ts          # interval checks, state-change alerts├── auth-store.ts       # saved storageState profiles (~/.browserbash/auth)├── pricing.ts          # cost_usd estimates (overridable price table)├── notify.ts           # webhook payloads (Slack autodetect)├── cache-store.ts      # builtin action-journal cache (re-templatized, origin-pinned, HMAC-signed)├── memory-store.ts     # run history: ordering + flaky report├── config.ts           # ~/.browserbash/config.json + credential resolution├── variables.ts        # {{var}} substitution, secrets masking└── output.ts           # NDJSON / human reporter

Adding a vendor = one file implementing BrowserProvider (connect() returning a Playwright Browser/Page) + one registry line in providers/index.ts.

License

Apache-2.0