Unfragile

The request "1b_chess" is ambiguous: it is not clear whether you want a chess engine, a chess analysis workstation, or a board-game project. For chess analysis and engine work, Stockfish 6 is a free open-source engine that analyzes positions and communicates via UCI, and Chess.ceo 2 offers a free workstation combining an opening explorer, Stockfish engine, game database and PGN management.

A question back: Do you want a chess engine to build or integrate, a chess analysis tool to use, or a chess variant game to play?

1
Stockfishstockfishchess.orgwebsite read, tools not yet checked
A free, open-source, cross-platform chess engine that analyzes and evaluates positions and finds the best move, communicating with apps over UCI 6.
Website
2
Chess.ceochess.ceowebsite read, tools not yet checked
A free chess analysis workstation with an opening explorer, the Stockfish engine, a game database and PGN management in one place 2.
Website
3
Sjengsjeng.orgwebsite read, tools not yet checked
A collection of chess and audio software written by its author, including chess programs listed on the site 7.
Website
4
Moddable Chess Enginemoddable.gameswebsite read, tools not yet checked
The engine behind Moddable.Games' Dungeon Chess, a chess variant reimagined as an asymmetric dungeon skirmish 3.
Website Docs
official:MCP server · Moddable Games Tools+1 community tools built for it

Sources

2Chess.ceo Free Chess Analysis Workstationchess.ceo · read 2026-10-29
3Moddable.Games Creating games you already ownmoddable.games · read 2026-10-29
6Stockfish - Strong open-source chess enginestockfishchess.org · read 2026-10-29
7Sjeng - chess, audio and misc. softwaresjeng.org · read 2026-10-29

For agents: the 10 actions behind this answer

game-engine · game-engine verified and signed
Expert skill for building web-based game engines and games using HTML5, Canvas, WebGL, and JavaScript. Use when asked to create games, build game engines, implement game physics, handle collision detection, set up game loops, manage sprites, add game controls, or work with 2D/3D rendering. Covers te
· Chess website read, tools not yet checked
Free chess analysis workstation. Opening explorer, Stockfish engine, game database, and PGN management in one place.
· Moddable.Games website read, tools not yet checked
The first board game company built entirely in the open. CC-licensed rulebooks, forkable engines, and original games designed to be taken apart.
sentry-instrument · sentry-instrument verified and signed
Instrument an application with Sentry — detect the platform, install and initialize the SDK if needed, and wire up any signal — error monitoring, tracing/performance, logging, metrics, profiling, session replay, user feedback, cron check-ins, uptime monitors for the deployed app, and AI/LLM monitori
· async-std website read, tools not yet checked
A Rust library for easy and understandable async programming
· Stockfish website read, tools not yet checked
Strong open-source chess engine
· Sjeng website read, tools not yet checked
· Context7 website read, tools not yet checked
Get the latest docs into Claude, Codex, Cursor and other agents. Context7 serves current, version-specific docs and code examples for any library.
c-library · ruamel.yaml.clib verified and signed
· Omnilib website read, tools not yet checked

Labels are the instruments' verdict and are never changed by ranking. Agents and robots get this same answer as JSON at /api/v1/find?q=…&answer=1 and through the MCP server.