Chess Game Analyzer — Find Blunders & Review Your Games Free
Run a full post-mortem on any chess game free with Stockfish. Import a PGN, enter your Chess.com or Lichess username, or set up any position with the board editor. Find every blunder and inaccuracy, review move-by-move — no signup, no daily limit.
📈 Evaluation Graph (Click any point to jump to that move)
Import a game or make moves to see the evaluation graph.
Turn Your Blunders into Lessons
Pinpoint Every Blunder and Mistake
See the exact moment your game turned. The analyzer scores every move by centipawn loss so you can measure the true cost of each blunder, mistake, and inaccuracy — not just guess where it went wrong.
Discover the Moves You Missed
Post-game analysis reveals what you could have played, not just what you did. See every hidden tactic, winning continuation, and engine-approved line — move by move across the whole game.
Reduce Your Average Centipawn Loss
Lower ACPL (Average Centipawn Loss) means more accurate chess. Review your games consistently and you'll recognize the tactical and strategic patterns that improve your rating the fastest.
Study Openings with a Live Explorer
See win rates, game counts, and ECO codes for every move. Identify where you first deviated from theory and build a stronger, better-prepared opening repertoire.
Prepare for Opponents and Tournaments
Load any game by username from Chess.com or Lichess. Set up positions from your opponent's games with the board editor, study their patterns, and arrive prepared.
Free, Unlimited — No Chess.com Diamond Needed
Get full Stockfish game review for every game, every time — no daily limit, no premium tier, and no account required. The analysis Chess.com charges for, free here with no restrictions.
Get Your Instant Post-Mortem in 3 Steps
Load Your Game or Position
Paste your PGN, enter your Chess.com or Lichess username to load recent games automatically, or use the FEN board editor to set up any specific position you want to review.
Stockfish Reviews Every Move
Stockfish evaluates every position in your game at configurable depth 10–30, scoring each move by centipawn loss. The evaluation bar updates in real-time and the analysis graph plots the whole game instantly.
Review, Learn, and Improve
Step through your game in the move list. Every blunder, mistake, and inaccuracy is flagged and graded automatically. Click any move to see what the engine scored it and why — then use practice mode to test yourself on similar positions.
Your Complete Chess Analysis Toolkit
- ✓ Full Game PGN Analyzer: Paste any PGN for a complete move-by-move post-mortem. Every move is scored, classified, and flagged — export the annotated PGN to study offline or share with your coach.
- ✓ Import by Username — Chess.com & Lichess: Enter your username on either platform and load any recent game directly. No copy-pasting required.
- ✓ Stockfish Game Review at Depth 10–30: The world-class engine trusted by grandmasters reviews your entire game and scores each position by centipawn loss.
- ✓ Move Classifications — Brilliant to Blunder: Every move is graded: Brilliant !!, Best, Excellent, Good, Inaccuracy ?!, Mistake ?, or Blunder ??.
- ✓ Accuracy Score & ACPL Report: See your overall accuracy percentage and average centipawn loss for the full game — the same metrics as Chess.com, free and unlimited.
- ✓ Opening Explorer with ECO Codes: Identify your opening by ECO code, browse win rates from the masters database, and see exactly where you deviated from theory.
- ✓ Evaluation Graph: The graph plots the centipawn evaluation across every move so you can spot the turning point of your game at a glance.
- ✓ Practice Mode — Guess the Move: Turn any game into an interactive training session. Play the position yourself and get instant feedback on your move classification.
- ✓ FEN Board Editor: Drag and drop pieces to set up any custom position. Load it from a FEN string or build from scratch — then analyze with Stockfish instantly.
- ✓ Shareable Position Links: Copy a unique URL for any board state and share it with teammates, students, or coaches — no account needed on either side.
- ✓ No Signup. No Daily Limit. Completely Free: Every feature is available without creating an account. Analyze as many games as you like with no restrictions.
Free Alternative to Chess.com Analysis
Chess.com limits free users to one game review per day and requires a Diamond subscription for full engine analysis. Here is how ChessNonStop compares:
| Feature | ChessNonStop | Chess.com Free | Chess.com Diamond |
|---|---|---|---|
| Games analyzed per day | Unlimited | 1 per day | Unlimited |
| Signup required | No | Yes | Yes |
| Engine depth | Depth 10–30 (configurable) | Limited | Deep |
| PGN import (full game review) | Yes | Yes | Yes |
| Username import — Chess.com & Lichess | Yes (both platforms) | Chess.com only | Chess.com only |
| Move classifications (Blunder, Mistake etc.) | Yes — 9 grades | Basic | Yes |
| Accuracy score & ACPL report | Yes | Limited | Yes |
| Opening explorer with ECO codes & win rates | Yes | Limited | Yes |
| FEN board editor | Yes | Yes | Yes |
| Practice / guess the move | Yes | No | Yes |
| Cost | Free | Free (limited) | ~$14/month |
How to Read Your Chess Analysis
The scores and classifications Stockfish produces have precise meanings. Here's what to look for when reviewing any game.
The Evaluation Score (+/−)
A positive score means White is better; negative means Black. +1.5 means White has roughly a 1.5-pawn advantage. 0.00 is equal. +3.00 or more is typically a winning position. A forced checkmate is shown as #N (mate in N moves).
Centipawn Loss & Move Grades
Centipawn loss measures how much your move differed from the engine's top-scoring choice. One centipawn = 1/100th of a pawn. A loss of 0–20 cp = Excellent; 20–60 = Good; 60–100 = Inaccuracy; 100–200 = Mistake; 200+ = Blunder. Brilliant moves are rare sacrifices the engine confirms as the strongest continuation.
Accuracy % and ACPL
Your accuracy percentage summarizes the whole game. 95%+ is excellent; 85–95% is good; below 75% indicates several costly errors. Average Centipawn Loss (ACPL) is the same measure in raw numbers — the lower your ACPL, the more accurate your play across the game.
Analysis Depth
Depth tells you how many half-moves (plies) ahead Stockfish calculated. Depth 18–22 is solid for most game reviews. Depth 28–30 is useful for critical endgame or tactical positions where shallow analysis can miss key lines.
ECO Code & Opening Theory
The ECO code (e.g. B20, E60) identifies your opening in the Encyclopedia of Chess Openings. The opening explorer shows the most popular continuations from masters' games and their win rates — helping you see where your preparation left the main line and what you deviated into.
Frequently Asked Questions
How do I analyze a chess game for free?
Paste your game's PGN into the Load Game tab, or enter your Chess.com or Lichess username to load recent games automatically. Stockfish starts reviewing every move the moment the game loads — no account, no payment, no daily limit.
Can I analyze my Chess.com games for free — without a Diamond subscription?
Yes. Enter your Chess.com username in the Load Game tab and select any game from your history. You get full Stockfish move-by-move analysis, blunder detection, accuracy scores, and all move classifications — the same features Chess.com locks behind its Diamond tier, completely free with no daily limit.
Can I analyze my Lichess games here?
Yes. Select Lichess from the platform dropdown in the Load Game tab, enter your username, and your recent games load automatically. You can also copy a PGN directly from Lichess and paste it in.
What is the difference between the Chess Analyzer and the Chess Calculator?
They serve two different purposes. The Chess Game Analyzer (this page) is for reviewing a complete game after you've played it — it scores every move by centipawn loss, flags all blunders and inaccuracies, produces an accuracy report, and identifies your opening. The Chess Calculator is for analyzing a single position instantly — paste a FEN, set the depth, and get the engine's evaluation of that one position. Use the Analyzer for post-game review; use the Calculator when you're stuck on a specific position.
What makes this a good free chess game analyzer?
Three things set it apart: no daily game limit (unlike Chess.com's 1-per-day free tier), no account required, and configurable Stockfish depth 10–30 so you can run quick overviews or deep post-mortems. It also includes features most free tools skip: an opening explorer with ECO codes and win rates, a practice mode to train from your own games, and both PGN and username import for Chess.com and Lichess.
What is a blunder in chess?
A blunder (??) is a move that loses significant material or decisive positional advantage — typically a centipawn loss of 200cp or more compared to the engine's top-scoring move. Blunders often include hanging a piece, missing a one-move tactic, or stepping into a forced checkmate. A mistake (?) is a smaller error (roughly 100–200cp loss); an inaccuracy (?!) is a suboptimal move that doesn't immediately change the outcome (60–100cp loss).
What is centipawn loss in chess?
Centipawn loss measures how much worse your move was compared to the engine's top-scoring choice. One centipawn equals 1/100th of a pawn's value. If the engine scores the top move at +1.50 and your move scores at +1.00, your centipawn loss is 50. Average Centipawn Loss (ACPL) across all your moves gives a single number reflecting your overall game accuracy — the lower your ACPL, the more accurate your play.
What is a good chess accuracy score?
Accuracy varies significantly by rating level. As a rough guide: 95%+ is excellent (grandmaster-level for that game); 85–94% is good (solid club-player quality); 75–84% is average; below 75% usually means several costly blunders or mistakes. Don't compare your accuracy directly to Chess.com's scores — the centipawn loss calculation methods differ slightly between platforms.
How does the blunder detection work?
After you load a game, Stockfish evaluates every position and scores each move by centipawn loss. Each move is then classified automatically: Brilliant, Best, Excellent, Good, Inaccuracy, Mistake, or Blunder. The Critical Moments panel highlights the biggest turning points. Click any move in the move list to jump directly to that position and see the engine's scoring alongside the alternative lines.
What is a brilliant move in chess?
A brilliant move (!!) is a rare, non-obvious move — often a sacrifice — that Stockfish confirms is the strongest continuation. The engine must evaluate it as the top choice at sufficient depth; a strong move in a routine position doesn't qualify. Brilliant moves are uncommon even in grandmaster games, which is exactly what makes them worth highlighting when they appear.
What is PGN and how do I use it?
PGN (Portable Game Notation) is the standard text format for recording a complete chess game. It looks like 1. e4 e5 2. Nf3 Nc6… and includes the full move history, player names, and result. On Chess.com, open your game, click "Share & Export", and copy the PGN. On Lichess, click the share icon and choose "PGN". Paste it into the Load Game tab here to start your full game review.
What is a FEN string?
FEN (Forsyth–Edwards Notation) encodes a specific board position as a single text string — for example, rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1. Use the FEN field in the Load Game tab to jump directly to any position for analysis. The board editor also exports the current position as a FEN so you can save or share it. To find the best move in a single FEN position (rather than reviewing a full game), use the Chess Calculator.
What is an ECO code?
ECO (Encyclopedia of Chess Openings) codes classify every opening into a 3-character code — for example, B20 (Sicilian Defence) or E60 (King's Indian Defence). The opening bar above the board shows the ECO code and opening name as you step through moves. The Opening Explorer tab uses ECO data to show which continuations are most popular from masters' games, along with their win rates.
How deep should I set the analysis depth?
For a standard game review, depth 18–22 gives reliable evaluations and runs quickly in the browser. Use depth 26–30 when you want to investigate a critical position in detail — a complex endgame, a sharp tactical sequence, or a critical opening line. Shallower depths (10–14) are useful for a fast first pass through a long game.
Is Stockfish the strongest chess engine?
Stockfish is consistently the strongest traditional chess engine in the world. Its NNUE (Efficiently Updatable Neural Network) evaluation gives it near-human positional understanding while maintaining exceptional tactical calculation. It is open-source, free, and the engine used by Lichess, Chess.com, and virtually every serious chess analysis platform.
How do I use game analysis to improve my rating?
The most effective routine: (1) Play a game. (2) Load it here immediately after and review every move the engine flagged as a mistake or blunder. (3) Don't just see what the engine scored — understand why: use the Opening Explorer for opening mistakes, check the Critical Moments panel for turning points, and use practice mode to test yourself on the positions you misplayed. Consistent post-game review is how players at every level reduce their average centipawn loss and raise their rating.
How do I share a position with someone?
Click the Share button in the toolbar (or "Copy Share Link" in the Load Game tab). This copies a unique URL to your clipboard that encodes the current board state as a FEN. Anyone who opens the link lands on exactly the same position, ready for analysis — no account required on either side.