Finally understand your chess games.
Promptfish is a grounded AI coach that lives right on lichess.org and chess.com, inside the analysis pages you already use. Every claim is checked against the real board and its Stockfish lines before it reaches you. The app is free; it runs on your own API key or the Claude subscription you already pay for.
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Free · your key or your Claude subscription · on the real Lichess & chess.com pages · live games blocked by design
See it coach on a real board
What it does
Coaching on the actual Lichess and chess.com pages, not a copy of them. Open any analysis board, study, or game review, ask about the position, and get a grounded answer with clickable moves that play out on the board, engine receipts on every claim, and follow-up buttons for the question you'd ask next.
There's a full game review too: every move classified from brilliant to blunder, an accuracy score, an estimated rating, and coaching on the move that turned the game.
Why
A generic chatbot will invent a knight fork that isn't on the board. Promptfish cannot: replies are built from the position's piece map, legal moves, and Stockfish lines, and claims that fail the check never reach you.
Free
No subscription and no paywall, now or later. Promptfish runs on your own AI key (OpenRouter, Groq, Anthropic, OpenAI, Gemini), so you pay only your provider for what you use: a fully coached game review costs about $0.02 with a budget model, not $15 a month.
Already paying for Claude? Connect Claude Code and it runs on your subscription, with no API key at all.
Fair play
Promptfish does not work during live games; the overlay stays dark by design. It coaches your analysis, your reviews, your preparation. What you win, you win alone.
Who it's for
Improving players who review their own games and want the why, not just the eval bar.
Access
Promptfish is in private beta. Request access and I'll send you the extension and the setup steps if it's a good fit.
Request sent. Your mail app opened a message to mdelrizzo@mun.ca. I read every one and reply by hand while the beta is small.
Coming to iOS
The same grounded coach, in your pocket. The iOS app runs Stockfish 18 on-device, with NNUE evaluation and no server round-trip, and it brings the full coached game review to your phone.
In development now. Request access to hear when it ships.
FAQ
Which sites does it work on?
Lichess and chess.com: analysis boards, studies, and game review pages. Live games are blocked by design; the overlay stays dark while a game is in progress.
Which AI providers can I use?
OpenRouter, Groq, Anthropic, OpenAI, or Gemini. Any key you already have works. Budget models work well because the position facts are supplied to the model, not guessed by it.
Can I use my Claude subscription instead of an API key?
Yes. Promptfish ships an MCP server that connects the overlay to Claude Code: your question routes to your own claude terminal and the grounded answer comes back to the board. No API key, no per-token cost, just the subscription you already have. Setup instructions come with your access.
Is my API key safe?
It is stored locally in your browser and requests go straight from your machine to the provider. There is no middleman server, and nothing of yours passes through us.
When does the iOS app ship?
It is in development now. Request access and I will let you know when it is ready to try.
Where's the code?
Promptfish is in private beta while it is finished, so it is not public yet. Contact for access and I will share the build and the setup steps.