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Parse & validate FEN board snapshots, PGN/SAN movetext (with parity, check/mate counts, threefold); compute Elo rating updates from win/draw/loss results, with Lichess/Chess.com tier bands
Details
For chess beginners, game-analysis students, and Chess.com/Lichess players. FEN mode: parses the 6 fields, validates 8 files per rank, one king per side, non-adjacent kings, no pawns on ranks 1/8, and renders the board. PGN mode: strips comments/variations/NAGs, validates each SAN move structurally, counts plies, and tallies checks / checkmates / castles. Elo mode: applies the standard formula E = 1/(1+10^((Ropp−R)/400)) and R' = R + K·(ΣS − ΣE) with opponents held at pre-event ratings (K=32 amateur default), plus Lichess/Chess.com community tier bands. Pure local, deterministic.
Execution
Fill in the form, run the tool, and review the result in one place.
Samples
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Tool usage guide
Chess FEN, PGN & Elo Rating Tutor analyzes FEN positions, validates PGN/SAN movetext, and calculates Elo rating changes from opponent ratings and game results. It runs locally and deterministically, with community tier bands for Lichess and Chess.com.
Background
A beginner wants to confirm that a FEN string represents the normal starting position before studying an opening.
Problem
Check the six FEN fields and verify that the board contains a valid arrangement of pieces.
How to use
Select FEN analysis and enter `rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1`.
Outcome
The tool validates the starting-position FEN and renders the corresponding chessboard.
Background
A student has a short PGN and wants to confirm the SAN sequence and summarize key move events.
Problem
Validate the movetext while checking the number of plies, castles, checks, checkmates, and result.
How to use
Select PGN analysis and enter `1. e4 e5 2. Nf3 Nc6 3. Bb5 a6 4. Ba4 Nf6 5. O-O Be7 1/2-1/2`.
Outcome
The tool checks the SAN structure and reports the move count, castling information, check or mate counts, and result.
It parses the six FEN fields and checks board structure, including eight files per rank, one king per side, non-adjacent kings, and no pawns on the first or eighth rank.
It removes comments, variations, and NAGs, validates SAN move structure, counts plies, and tallies checks, checkmates, castles, and the game result.
It uses the standard expected-score formula and applies R' = R + K·(ΣS − ΣE), with opponent ratings fixed at their pre-event values.
The default K-factor is 32, and it can be changed from 1 to 60.
No. The tier bands are community estimates; Lichess uses Glicko-2 and Chess.com uses Glicko-1 rather than standard Elo.
Background
A player rated 1613 completes five games against opponents rated 1609, 1477, 1388, 1586, and 1720.
Problem
Estimate the post-event rating after three wins and two losses.
How to use
Select Elo calculation, enter player rating `1613`, use K-factor `32`, and add `1609 loss`, `1477 win`, `1388 win`, `1586 win`, and `1720 loss` in the games field.
K-factor: 32Outcome
The projected new rating is approximately 1617, based on the standard Elo formula with opponent ratings held at their pre-event values.