Mantis

Lets AI agents browse the web as short, numbered text instead of screenshots.

perzian.dev/mantis · by Perzian

It works with Claude Code, Codex, Cursor or your own agent as an MCP server. Install in two commands.

npx -y -p mantis-browser mantis install
claude mcp add mantis -- npx -y -p mantis-browser mantis-mcp
npx -y -p mantis-browser mantis read https://example.com   # try it without an agent

Windows, Linux servers and other agents: SETUP.

One real task (Luna, each tool’s median run of 5 by input tokens, replayed): about half the time, over 3.5x fewer input tokens, less than half the calls. Across all 5 runs: 3-5x fewer tokens, about half the time, 11-12 calls vs 21-29. This is a selected example from 16 long tasks; medians across all 16 are in Results. Full video.

Security and threat model: SECURITY.md.

How it works

Related MCP server: browser-mcp

What the agent sees

Results

Mantis vs the accessibility tree (Playwright MCP) on public sites, gpt-6-luna and claude-haiku-5-5. Every cell is a per-run median; time is end-to-end wall time per run:

0.1.13: headline numbers are 0.1.9's; later builds checked on Dickens (Luna, Haiku), the capability-v1 local set and the visual-live-v1 real-site set.

Long tasks (correct: 14 keyed tasks, 42 runs per cell; medians: all 16 tasks, 48 runs per cell; both approaches run in the same session):

Short tasks (30 tasks, 90 runs per cell; tree and screenshot columns are the earlier 20261026 run):

Versus the accessibility tree:

• Long tasks: accuracy within one run, 29-47% fewer input tokens, 29-37% fewer calls, about a third less time.

• Short tasks: accuracy equal or better, 35-57% fewer input tokens.

Versus screenshots:

• Luna: screenshots score 2 runs higher but use more tokens and time.

• Haiku: screenshots use fewer tokens.

Caveats:

• Short-task times compare a newer Mantis build with the earlier tree and screenshot run, so treat that time gap as indicative.

• Scores come from deterministic answer keys on the final page state. Two long iframe/tab tasks can't be keyed and are left out of the long-task counts.

• Method and full caveats: bench/RESULTS.md.

Use your own Chrome

Optional. Mantis can drive your real Chrome (your tabs, your sign-ins) instead of launching a fresh browser:

• Run npx -y -p mantis-browser mantis chrome. It starts Chrome on 127.0.0.1:9222 with a dedicated profile.

• Mantis automatically attaches while that Chrome is running. Set MANTIS_CDP_URL only when Chrome uses another debugging port.

• Sign in to your sites once in that profile; sign-ins persist there.

• Mantis then acts on your real tabs, so act carefully. Set MANTIS_AUTO_ATTACH=0 to always launch a fresh browser.

Limitations

• No canvas input: canvas, WebGL, maps and drawing apps are described only as canvas, with no coordinate click or draw tool.

• Login and bot walls need ask_human, which needs a display.

• Benchmarked only on read, navigate and form-fill tasks on public sites, with two models. The screenshot baseline is this project's own tool, and a few tasks were swapped after results (disclosed).

• Page content is untrusted data; see SECURITY.md.

• Small v0.1.x beta.

Learn more

• How it works in detail

• Claude skill: teaches Claude how to read Mantis output

• Install, configuration and tool reference

• Re-running the benchmarks

License

MIT