How to Analyze Your Chess Games and Practice Blunders on ChessBlunders.org

Updated

ChessBlunders.org is a web tool that runs your games through Stockfish 16 to flag your blunders, then converts those mistakes into puzzles you can drill. The workflow is: get your game into the site, let the engine analysis mark the blunders, practice the resulting puzzles, and carry the lesson back to your real games. This guide covers each step and the points where people usually get stuck.

What the site does

The core loop has three parts:

  1. Analysis — Stockfish 16 reviews your game and identifies blunders.
  2. Conversion — each flagged blunder becomes a practice puzzle.
  3. Practice — you solve the positions repeatedly until the correct move sticks.

The point is that you are not studying generic tactics. You are studying the exact positions where you went wrong, which makes the repetition more relevant than a random puzzle set.

Step 1: Get your game into the site

You need the moves of a game you actually played. The standard format for this is PGN (Portable Game Notation), the plain-text format most chess sites and apps export.

To get a PGN:

  • Online (Lichess, Chess.com, etc.): open the game in your archive and look for an export, download, or "copy PGN" option.
  • Over the board or in an app: if the app stores your games, export from its game list. If you played offline, you'll need to enter the moves manually into any PGN editor first.

Once you have the PGN text, paste or upload it into ChessBlunders.org to submit the game for analysis. The site's own description states it analyzes games with Stockfish 16, so expect the engine to run on the position after each move.

Expected result: the game appears in your list with an analysis status. When analysis finishes, blunders are marked.

Common snag: a PGN that is missing headers, has illegal moves, or is truncated will fail to import. If a game won't load, re-export it from the source rather than editing it by hand.

Step 2: Understand how blunders are flagged

Stockfish 16 evaluates every position and assigns a score. When your move causes the evaluation to swing sharply against you, that move is a candidate blunder. In practice:

  • A move that turns a roughly equal position into a clearly losing one is the classic blunder.
  • Smaller swings are usually labeled as mistakes or inaccuracies rather than blunders.

The exact thresholds are set by the site, so treat the labels as a guide to where to look, not as a verdict on your chess. A move the engine calls a blunder may have been a reasonable practical try in a lost position — the value is in seeing what the engine preferred and why.

What to check on each flagged move:

Question Why it matters
What was the engine's suggested move? Shows the idea you missed.
What tactic or threat did I overlook? Identifies the pattern to drill.
Was it a calculation error or a positional misjudgment? Tells you whether to practice tactics or study plans.

Step 3: Turn blunders into puzzles

This is the part that separates ChessBlunders.org from a plain analysis board. Each blunder you made is converted into a puzzle: you are shown the position and asked to find the better move. Because the position comes from your own game, you already have the context — you know what you were thinking, which makes the correction more memorable.

Work through them like this:

  1. Solve without hints first. Try to find the move yourself before revealing the answer.
  2. Compare with what you played. The gap between your move and the correct one is the lesson.
  3. Repeat the set. Spaced repetition is what moves a pattern from "I know it" to "I play it."

Common snag: treating the puzzles as a score to maximize. The goal is recognition, not a high solve rate on the first pass. Missing the same puzzle twice is useful information — it means that pattern hasn't stuck yet.

Step 4: Take it back to your games

Analysis and puzzles only pay off if they change what you do at the board. A simple routine:

  • After each serious game, submit it and review the flagged blunders the same day, while you still remember your thinking.
  • Note the type of error — a missed fork, a back-rank weakness, a premature pawn push — rather than the specific move.
  • Before your next game, review your recent puzzle set as a warm-up.

If the same category of blunder keeps appearing, that is your study priority, not the individual moves.

Quick reference

Stage Input Action Result
Import PGN of your game Paste/upload to the site Game queued for analysis
Analyze Game moves Stockfish 16 evaluates each position Blunders flagged
Practice Flagged blunder Solve as a puzzle Pattern reinforced
Apply Your next games Review recurring error types Fewer repeats

FAQ

Do I need an account? The site is built around submitting and storing your games, so expect to need an account to keep a history of analyzed games and puzzles. The available information doesn't specify login requirements, so check the site directly.

Is it free? The source material doesn't state pricing. Don't assume it's free — verify on the site before relying on it.

What engine does it use? Stockfish 16, per the site's own description.

Can I use it for games I didn't play? The value is in analyzing your own games, since the puzzles are generated from your mistakes. Analyzing someone else's game gives you puzzles that don't target your weaknesses.

How many games should I submit? Start with your most recent loss or a game where you felt you threw away a good position. One well-reviewed game beats ten unreviewed ones.