Chess ECO Codes Lookup & Explorer (A00-E99)
If you have ever seen a code like E20, C42 or B90 beside a game score, that code is a shortcut for the opening family. ECO codes help players browse databases, sort opening statistics, and recognise what opening a game belongs to without reading every move from scratch.
Quick answer: ECO stands for Encyclopaedia of Chess Openings. The system runs from A00 to E99, with five broad opening volumes and 500 main code slots.
Use the quick checker below if you want a fast code-to-opening answer. Then scroll down for the full A-to-E family map.
Quick ECO lookup
Type a code to get a fast answer. This is especially handy for searches like E20 opening name, E12 opening name, C42 opening name, D40 opening name and E00 opening name.
Most-searched ECO code answers
Nimzo-Indian Defense
E20 is the Nimzo-Indian family entry point.
Typical route: 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4
Queen's Indian Defense
E12 belongs to the Queen's Indian family.
Typical route: 1.d4 Nf6 2.c4 e6 3.Nf3 b6
Petrov Defense
C42 is the Petrov, also called the Russian Defense.
Typical route: 1.e4 e5 2.Nf3 Nf6
QGD: Semi-Tarrasch Defense
D40 is a Queen's Gambit Declined Semi-Tarrasch code.
Typical route: 1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.Nf3 c5
Early Indian systems with ...e6
E00 is an early branching code rather than one single famous named line.
Typical route: 1.d4 Nf6 2.c4 e6
Italian Game
C50 is the starting code for the Italian family.
Typical route: 1.e4 e5 2.Nf3 Nc6 3.Bc4
Important: an ECO code is a filing label, not a complete understanding of the opening. Two games can share a broad family code and still lead to very different middlegames a few moves later.
Jump straight to the opening volume you want to browse.
How the ECO system is organised
The ECO system splits opening theory into five letter groups. In broad terms, A covers many irregular and flank openings, B covers semi-open defenses like the Sicilian and Caro-Kann, C covers 1.e4 e5 and the French, D covers 1.d4 d5 structures and the Grünfeld, and E covers Indian systems built around ...e6 or ...g6.
That means the letter gives you the big opening world first, while the numbers narrow the game into a more specific family. So E20 and E51 both live in the Indian-defense universe, but they point to different branches inside that world.
How to use ECO codes without getting lost
The best way to use ECO codes is as a navigation tool. If you see B90, you immediately know you are in the Najdorf family. If you see C50, you know the game has entered the Italian family. That saves time when sorting databases, comparing opening results, or finding model games.
The trap is assuming that one code tells the whole story. It does not. ECO codes help you get to the right neighborhood. You still need the key plans, pawn structures and tactical ideas inside that neighborhood.
Common questions about ECO codes
Basics and meaning
What are ECO codes in chess?
ECO codes are a standard way to classify chess openings. The system runs from A00 to E99 and groups openings into five big volumes so players and databases can label games quickly.
What does ECO stand for in chess?
ECO stands for Encyclopaedia of Chess Openings. When players talk about an ECO code, they mean the opening classification label attached to a game or opening line.
How many ECO codes are there in chess?
There are 500 main ECO codes in the standard system. They run from A00 to E99, which gives five letter groups with one hundred numbered slots in each group.
How do ECO codes work?
ECO codes work like filing labels for openings. The letter points to a broad opening volume and the two digits narrow the game down to a specific family or sub-family.
That is why a code like C50 tells you “Italian Game family,” while a later code inside the same volume can point to a more specialised branch.
Exact code lookups
What opening is ECO E20?
E20 is a Nimzo-Indian Defense code. The typical route is 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4, after which more specific Nimzo-Indian branches get later E-codes.
What opening is ECO E12?
E12 is a Queen's Indian Defense code. A common route is 1.d4 Nf6 2.c4 e6 3.Nf3 b6, with E12-E19 covering the broader Queen's Indian family.
What opening is ECO C42?
C42 is a Petrov Defense code. The base move order is 1.e4 e5 2.Nf3 Nf6.
What opening is ECO D40?
D40 is a Queen's Gambit Declined, Semi-Tarrasch Defense code. A typical route is 1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.Nf3 c5.
What opening is ECO E00?
E00 is an early Indian-systems code after 1.d4 Nf6 2.c4 e6. It covers Queen's Pawn Game style positions before the game branches into more specific Catalan, Queen's Indian or Nimzo-Indian codes.
Families and misconceptions
What is the ECO code for the Queen's Indian Defense?
The Queen's Indian Defense lives mainly in E12-E19. If you see one of those codes, you are usually looking at a Queen's Indian line.
What is the ECO code for the Italian Game?
The Italian Game begins at C50. The broader Italian and Two Knights family sits in the C50-C59 range.
Are ECO codes the same as opening names?
No. An ECO code is a classification label, while the opening name is the human-readable name of the opening or variation. Many related lines can sit inside the same broad ECO family.
Does one ECO code always mean one exact position?
No. An ECO code usually points to an opening family or branch, not one frozen board position. Two games can share a code for several moves and still diverge soon after.
Is memorising ECO codes enough to understand openings?
No. Memorising ECO codes can help you organise study, but it does not replace understanding plans, pawn structures, tactical themes and typical middlegames.
Why do players and databases use ECO codes so much?
Players and databases use ECO codes because they are quick, compact and standardised. A short code lets you sort thousands of games by opening family much faster than reading every move manually.
ECO codes are useful for finding opening families quickly, but they are best used as a study map rather than a substitute for understanding the ideas.
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