Open-source browser MCP returns numbered elements and diffs, cutting tool output 3-6x
Silent_Sky6043 · reddit · 2026-10-27
The author released Mantis, a free open-source browser MCP server that hands the agent a short numbered list of page elements instead of the full accessibility tree, and returns only what changed after each action.
Results (author's own runs)
- About 3-6x less tool output than the Playwright MCP tree on short tasks.
- Equal or better accuracy on 30 real-site tasks: Luna 88 vs 86, Haiku 90 vs 88 out of 90.
Caveats
- Two long chain tasks were excluded, and some tasks were swapped after the fact (disclosed in the repo).
- Page text is treated as untrusted; see SECURITY.md.
Install: claude mcp add mantis -- npx -y -p mantis-browser mantis-mcp, then npx -y -p mantis-browser mantis install.
Related event: Open-Source Mantis Browser MCP Cuts Token Use With Numbered Text(2 posts)→
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