ECO codes A00 to E99

The ECO system files every chess opening under one of 500 codes in five volumes. Here are all of them with the 3,690 named lines behind them, or browse the openings A–Z. What ECO codes are is explained below the list.

A: Flank Openings A00–A99

B: Semi-Open Games B00–B99

C: Open Games C00–C99

D: Closed & Semi-Closed Games D00–D99

E: Indian Defenses E00–E99

What are ECO codes?

ECO stands for the Encyclopaedia of Chess Openings, a reference work on opening theory published by the Serbian company Šahovski Informator (Chess Informant). Its first edition came out in five volumes between 1974 and 1979: C in 1974, B in 1975, D in 1976, E in 1978 and A in 1979. The lines in it are taken from master games and from analysis published in Informant, chosen by editors who are mostly grandmasters. Its chief editor from the first edition on was Aleksandar Matanović (1930–2023).

Instead of the traditional opening names, the encyclopaedia uses codes: a letter from A to E for each of the five volumes, followed by a number from 00 to 99, 500 codes in all. Other chess publications and websites took up the system, and "ECO" is often used as shorthand for the codes themselves. "ECO code" is a registered trademark of Chess Informant.

What the five volumes cover

A, flank openings: the English, the Réti, Bird's Opening, the Dutch, the Benoni, the Benko Gambit, the Old Indian and irregular first moves.
B, semi-open games other than the French: the Sicilian, the Caro-Kann, the Pirc, the Modern, Alekhine's Defense and the Scandinavian.
C, open games and the French: the Ruy Lopez, the Italian Game, the Scotch, the Four Knights, Petrov's Defense, the Philidor, the Vienna, the King's Gambit and the French Defense.
D, closed and semi-closed games: the Queen's Gambit, accepted and declined, the Slav, other Queen's Pawn games and the Grünfeld.
E, Indian defenses other than the Grünfeld and the Old Indian: the Nimzo-Indian, the Queen's Indian, the King's Indian, the Bogo-Indian and the Catalan.

ECO codes on this site

The codes here come with the Lichess chess-openings dataset, which gives each of its 3,690 named lines one code. A code usually holds several named lines, and a big opening fills many codes: the Sicilian Defense has lines under every code from B20 to B99. 498 of the 500 codes have at least one named line; D72 and D73 have none.

How to find the ECO code of a game

Paste the game's moves or its whole PGN into the opening identifier, or play the first moves on its board. It names the longest named line the game follows, with its ECO code, and the move with which the game leaves the named lines.