Chess game analysis
Find out which chess move lost the game
You played, you lost, and the engine gave you a number. Checkup pulls your games straight from your Chess.com account and tells you which move cost you the game, and why, in words you can actually use next time.
What you get
The move that cost you
A chess engine will happily flag thirty moves in one game. Most of them did not matter. Checkup ranks what it finds by how much the position actually swung, and puts the two or three moves that decided the result at the top of the report.
Why it was wrong
Every flagged move comes with a written explanation: what you missed, what the position asked for instead, and how the game would have gone. The explanation is built from the engine's own best line, so it describes moves that exist rather than moves that sound plausible.
Your patterns, not just this game
One game tells you little. Across your whole history, Checkup shows which phase of the game costs you most, which openings you keep losing with, and where in a game your accuracy starts to drop.
Your games, one username away
Give Checkup your Chess.com username and it fetches your games itself, through the public Chess.com API. No exports, no PGN files to upload, no password, no account linking.
A report you keep
Each analysis is a single self-contained page with the board, the moves, and the explanations. Nothing loads from a server when you open it later.
Coming next
Opening repertoire analysis, so you know the exact move where you leave theory. Targeted exercises built from your own weak spots. Lichess import alongside Chess.com. None of this exists yet, and this page will say so until it does.
Why you can trust it
Chess tools built on language models invent moves. They describe captures that are not available and mating nets that do not exist. Checkup checks every move an explanation names against the actual position on the board, and refuses to show the ones that are not legal.
Analysis is also reproducible. The engine runs at a fixed search depth, so the same game gives you the same report today and next month. A tool that quietly changes its verdict between runs cannot teach you anything.
Known limits
- There is no "Brilliant" badge and there never will be. Checkup reports what went wrong. It does not hand out compliments.
- One kind of error is checked: a move that does not exist in the position. A legal move described with the wrong consequence is not caught today.
- Chess.com only, for now. Lichess import is planned, not built.
- Checkup will not make you a better player on its own. It tells you what happened. The work is still yours.
Questions
Is Checkup free?
Pricing is not decided yet. The analysis engine behind Checkup is open source under the AGPL, so anyone who wants to run it themselves can. The hosted version is what we are building now.
Do I need to give my Chess.com password?
No, and there is no field to type one into. Chess.com publishes a public API for data that anyone can already see without logging in. Checkup reads your games through it, using nothing but your username.
Does it work with Lichess?
Not yet. Chess.com import works today. Lichess is the next source we plan to add, and this page will change the day it does.
How is this different from the game review I already get?
Most reviews give you a number and a label per move. Checkup is built around the small number of moves that changed the result, explains them in words, and tells you plainly what it cannot measure.
What engine does it use?
Stockfish, running at a fixed search depth. The depth and the thresholds used to classify a move are written into every report, so you can always see what produced a given verdict.
Will it tell me my move was brilliant?
No. There is no brilliant class. Checkup finds mistakes and missed wins, which is where the improvement is.
Waitlist
Checkup is not open yet. Leave an email, we will confirm it, then write once more the day it opens. Nothing in between.
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