unbrowser by Unchained MCP Server

unbrowser

The cheap browser pass for agents. One native binary. No Chrome.

Official MCP Registry identity: mcp-name: io.github.protostatis/unbrowser

unbrowser is a stateful, non-visual web runtime for agents. It sits between curl/WebFetch and a real browser: it retains cookies and DOM state, returns queryable element refs, handles links and HTML forms, detects challenge and SPA signals, and can run bounded QuickJS page scripts when static HTML is not enough.

Default navigate is a fast static/SSR pass. Set exec_scripts: true only when you need bounded QuickJS execution. Heavy SPAs, pixels, V8 fidelity, extensions, and interactive anti-bot challenges belong in a real Chrome tier.

Try the live public-web demo before installing. It accepts only the fixed public source sets shown on the page; do not send private data, cookies, or authenticated tasks through it. A shared Streamable HTTP MCP endpoint is available at https://unchainedsky.com/unbrowser-mcp for public smoke tests; production sessions should use a local install.

Use unbrowser only on sites, accounts, and data you are permitted to access. Challenge detection and cookie import do not grant permission to bypass access controls or site terms. Treat session cookies as credentials: keep them local, scope them to the authorized task, and never send them to the public demo.

Pick the right tier

Need	curl / WebFetch	unbrowser	Real Chrome
Static / SSR HTML	raw response	structured BlockMap + DOM queries	full browser
Cookies, links, HTML forms	DIY	built in	built in
Client-side page scripts	❌	bounded QuickJS, opt-in	V8
Pixels, Canvas, WebGL, Workers, extensions	❌	❌	✅
Agent-oriented output	DIY parsing	element refs, page signals, structured extraction	DIY CDP / DOM parsing
Interactive access challenge	❌	detect + stop or escalate	authorized browser / human confirmation

Use unbrowser when HTTP alone is too dumb and a full browser is too expensive. When the page needs Chrome, the output tells the agent to escalate rather than pretending compatibility it does not have.

Quick start

Docker — Linux amd64/arm64, ~13 MiB pull

docker pull ghcr.io/protostatis/unbrowser:latest

# One-shot navigation
docker run --rm ghcr.io/protostatis/unbrowser:latest \
  navigate https://example.com --json

# Default mode: MCP over stdio
docker run --rm -i ghcr.io/protostatis/unbrowser:latest

The image is distroless and runs as non-root: no shell, package manager, or persistent state. Pin :vX.Y.Z or an image digest in production.

Python

pipx install pyunbrowser   # recommended on macOS / modern Linux
# or, inside a Python 3.10+ virtual environment:
pip install pyunbrowser

from unbrowser import Client

with Client() as ub:
    ub.navigate("https://news.ycombinator.com")
    for link in ub.query(".titleline > a")[:3]:
        print(link["text"], link["attrs"]["href"])

On macOS, /usr/bin/python3 is 3.9 and cannot install the wheel; use pipx or a Homebrew Python. The PyPI distribution is pyunbrowser, while the import and executable remain unbrowser.

MCP

{
  "mcpServers": {
    "unbrowser": {
      "command": "unbrowser",
      "args": ["--mcp"]
    }
  }
}

Minimal surface: add "--mcp-profile", "minimal" to expose only navigate/query/extract/help and let the agent discover the rest via help(topic). The Python wrapper ships a 3-tool smart server (search/open/help) as the unbrowser-smart console script.

<details> <summary>Docker MCP configuration</summary>

{
  "mcpServers": {
    "unbrowser": {
      "command": "docker",
      "args": [
        "run", "--rm", "-i",
        "ghcr.io/protostatis/unbrowser:latest"
      ]
    }
  }
}

</details>

See installation and interface reference for Cargo, release archives, source builds, persistent shell sessions, raw JSON-RPC, and all MCP options.

What an agent gets

• navigate returns a BlockMap: page title, landmarks, headings, interactives, density signals, and an ASCII outline. Its size is page-dependent; it is structured for planning rather than a fixed-token promise.
• Stable element refs (e:142): query an element once, then click, type, or submit it without re-parsing HTML.
• Stateful cookies and forms: cookie jar, GET and URL-encoded POST form submission, links, and redirects persist within a session.
• Page and challenge signals: density.likely_js_filled, thin_shell, and challenge.provider tell an agent whether to run scripts, inspect embedded data, stop, or escalate to an authorized browser session.
• Routing aids on every result: micro_hint (the single next concrete step), next_tools (ranked candidates), avoid (tools with nothing to act on), and a stable escalation taxonomy (challenge, thin_shell, partial_result, …) with retryable/severity/evidence — recommendations never contradict avoid.
• Structured helpers: route discovery, card extraction, table normalization, text_main, and selector debugging cover common extraction workflows.

Script mode and escalation

{"id":1,"method":"navigate","params":{"url":"https://example.com","exec_scripts":true}}

With exec_scripts: true, inline and external scripts run in QuickJS under a bounded watchdog. This can materialize light hydration and fetch-visible data; it is not V8 or a rendering engine. Heavy React/Vue/Ember apps may still leave an empty shell.

Escalate to unchainedsky-cli or Unchained when a permitted task needs real pixels, Canvas/WebGL, Workers, browser extensions, V8 compatibility, an authenticated profile, or human confirmation. When the user has already established an authorized session in Chrome, cookies_set can import the required session cookie locally until it expires; it is not a license to circumvent a site's controls.

Documentation

Need	Read
Install paths, session CLI, one-shot CLI, raw RPC, MCP, shims, full RPC table	Usage reference
Script compatibility, SPA signals, challenge handling, authorized cookie handoff, escalation	Compatibility and escalation
Distribution and supported directory listings	Distribution notes
Build the native binary	Build instructions

License

Apache-2.0 — see LICENSE.