Browser39

browser39

A headless browser for AI agents that fetches modern web pages, runs JavaScript, manages sessions, and returns token-efficient Markdown.

• Handles modern sites. Executes JavaScript, fills forms, queries the DOM, persists cookies and sessions across runs.
• LLM-usable output. Compact Markdown with content preselection, so the agent reads the section it needs, not the whole page.
• Local-only. No data sent to third-party services.
• Single binary. No Chrome, no Puppeteer. ~52MB. macOS, Linux, Windows.

Comparison

	browser39	Playwright / Puppeteer	Raw HTTP (requests, ureq)
External browser	None (single binary)	Requires Chrome/Chromium	None
Binary size	~52MB	~280MB with browser	N/A (library)
Platforms	macOS, Linux, Windows	macOS, Linux, Windows	Any
JavaScript	Yes (V8 via deno_core)	Yes (full V8)	No
HTML to Markdown	Built-in, token-optimized	No (raw HTML or screenshots)	DIY
Token preselection	Content sections, agent picks what to read	No	No
Cookies & sessions	Automatic, persisted, encrypted	Manual	Manual
DOM queries	CSS selectors + full JS DOM API	Full DOM API	No
Forms	fill + submit	Full interaction	Manual POST
Auth & secrets	Profiles, redaction, opaque handles	Manual	Manual
Transports	MCP (stdio + HTTP), JSONL, CLI	Library API	Library API

Token savings in practice

Real test: extracting the "Optical communications" section from [Artemis II on Wikipedia](https://en.wikipedia.org/wiki/Artemis_II) (full page: ~14,600 tokens).

| | Raw HTTP | WebFetch (Claude Code built-in) | [Mistral Web Search](https://docs.mistral.ai/agents/tools/built-in/websearch) | browser39 | |--|----------|-------------------------------