Chess ECO Codes Lookup & Explorer (A00-E99)

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, books and databases can label opening families quickly.

The system is useful because it gives one shared reference language across huge numbers of games. Use the quick ECO lookup above for a fast answer, then use the A-E family map below to place the code in its wider opening world.

ECO stands for Encyclopaedia of Chess Openings. When players mention an ECO code, they mean the standard classification label attached to an opening or opening branch.

The term matters because many databases, tournament files and opening indexes use the code instead of the full opening name. Use the lookup tool on this page if you want to convert a code into a readable opening family fast.

There are 500 main ECO code slots in the standard system. The codes run from A00 to E99, which creates five letter groups with one hundred numbered slots in each group.

That structure is one reason the system has lasted for so long: it is compact, memorable and easy to sort in databases. The volume sections on this page show how those 500 slots are distributed across the main opening families.

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 more specific family or branch.

That means a code such as C50 tells you the game belongs to the Italian family, while a later code in the same volume points deeper into a branch. Use the quick answer cards and the A-E map here to move from broad family to finer classification without getting lost.

Chess players use ECO codes because they are a fast, standard way to group similar openings. A short code lets you sort games, opening files and statistics much faster than reading every move order from scratch.

The code is especially helpful when one opening has many naming variations across books and websites. Use the lookup box on this page to turn an unfamiliar code into a family name before you dig into specific lines.

Yes, ECO codes are still widely used today in databases, game collections, opening indexes and tournament references. They remain one of the most common ways to organise opening material.

That staying power comes from the fact that the system is short, stable and easy to scan across thousands of games. The family map on this page helps you connect those familiar codes to the opening groups they represent.

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 receive later E-codes.

E20 is one of the most important “gateway” codes because it marks entry into a huge and theory-rich opening family. Use the lookup tool and the Volume E section below to see how E20 connects to later Nimzo-Indian branches.

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.

E12 matters because it quickly separates Queen's Indian structures from nearby Indian systems that begin with similar early moves. Use the quick lookup and the Volume E guide here to compare E12 with E00 and E20.

C42 is a Petrov Defense code. The base move order is 1.e4 e5 2.Nf3 Nf6.

C42 is a good example of how a compact code can identify a famous opening immediately without listing moves in full. Use the lookup box and the Volume C section on this page to place the Petrov inside the wider 1.e4 e5 universe.

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.

D40 is useful because it points to a recognisable strategic branch inside the larger Queen's Gambit Declined family. Use the quick lookup and the Volume D breakdown below to see where the Semi-Tarrasch sits among neighboring d4 d5 structures.

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.

E00 is important because it often marks a crossroads rather than one fixed named opening. Use the quick answer card for E00 and then compare it with the later Volume E families to see how the position can branch.

C50 is the starting ECO code for the Italian Game family. The typical route is 1.e4 e5 2.Nf3 Nc6 3.Bc4.

C50 is a good reminder that some famous openings occupy a whole range rather than a single isolated slot. Use the lookup tool here and then browse Volume C to see how the Italian family sits beside the Scotch, Petrov and Ruy Lopez.

B90 is a Sicilian Najdorf code. A typical route is 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6.

B90 is one of the best-known ECO labels in modern opening theory because it points to a huge body of sharp, highly studied games. Use the lookup and the Volume B section below to place B90 inside the wider Sicilian family.

E24 is a Nimzo-Indian Defense, Sämisch family code. A typical route is 1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.a3.

E24 is especially useful for lookup because it takes a player from the broad Nimzo umbrella into a more specific branch immediately. Use the lookup tool and the Volume E family map to compare E24 with the broader E20 entry point.

The letters A to E mark the five major ECO volumes. Each letter groups a broad opening world before the numbers narrow the line to a family or branch.

The letters matter because they tell you the big picture before you study the exact code. Use the volume navigation on this page to jump straight to A, B, C, D or E and see the family context around any code.

Volume A mainly covers irregular openings, flank openings, many early d4 sidelines, Benoni and Benko families, and the Dutch Defense. It includes codes such as A00, A10 and A80.

Volume A is broader and more varied than many beginners expect, which is why it often feels less tidy than later volumes. Use the Volume A section here to see how those offbeat and flank systems are grouped.

Volume B mainly covers semi-open defenses against 1.e4, including Alekhine lines, Modern and Pirc families, the Caro-Kann, and the Sicilian Defense. It is the home of codes such as B10 and B90.

That makes Volume B one of the most practical parts of ECO for players who face 1.e4 regularly. Use the Volume B map below to see how the Caro-Kann and Sicilian families are separated inside the same broad volume.

Volume C covers the French Defense and the large 1.e4 e5 open-game universe. It includes families such as the King's Gambit, Petrov, Scotch, Italian Game and Ruy Lopez.

Volume C is especially useful because many famous classical openings live close together there. Use the Volume C section on this page to compare C42, C50 and the later Ruy Lopez codes quickly.

Volume D covers many closed games after 1.d4 d5, including early Queen's Pawn systems, Queen's Gambit Accepted, Queen's Gambit Declined, Slav and Semi-Slav branches, and the Grünfeld family in the later D-codes.

That mix can surprise players who expect the Grünfeld to live with the other Indian systems. Use the Volume D map here to see how d4 d5 structures and the Grünfeld are arranged in one place.

Volume E covers Indian systems built around ...e6 or ...g6, including the Catalan, Queen's Indian, Nimzo-Indian and King's Indian families. It includes important codes such as E00, E12, E20 and E89.

Volume E is one of the most searched parts of the ECO map because so many major d4 openings branch there. Use the Volume E section on this page to compare the early crossroads code E00 with the later family codes.

The Queen's Indian Defense mainly lives in E12-E19. If you see a code in that range, you are usually looking at a Queen's Indian line or very nearby branch.

This range matters because the early move order can resemble other Indian systems before the structure becomes clearer. Use the lookup tool and the Volume E block here to compare E12-E19 with E20-E59.

The Nimzo-Indian Defense mainly lives from E20 to E59. E20 is the broad entry point, while later codes narrow the game into major Nimzo branches.

That wide range shows how deep and varied the Nimzo-Indian really is. Use the quick lookup on this page to test codes such as E20, E24 and E51, then read the Volume E family map for context.

The King's Indian Defense mainly lives from E60 to E99. Those codes cover the major King's Indian branches once the opening has clearly entered that family.

This range is important because players often confuse late Volume E with the Grünfeld, which is handled elsewhere. Use the Volume E section below to place King's Indian codes correctly before comparing them with late Volume D.

The Italian Game mainly begins at C50, and the broader Italian and Two Knights family sits in the C50-C59 range. That range covers the major branches after 1.e4 e5 2.Nf3 Nc6 3.Bc4.

The range is useful because many players search for “C50 opening name” when they really want the whole family picture. Use the C50 answer card and the Volume C map here to see the Italian family in context.

The Sicilian Defense mainly occupies B20-B99. Earlier parts of that range include anti-Sicilians and closed systems, while later parts include major branches such as the Dragon and Najdorf.

This is one of the widest and busiest ECO territories in the whole system. Use the Volume B guide on this page to see how broad Sicilian territory is before drilling into a narrower code such as B45 or B90.

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.

That is why one code can point to a family label even when players still debate exact naming for a sub-variation. Use the lookup box on this page to move from the code to the family name first, then study the line more deeply.

No. One 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.

This is a common misunderstanding because the code looks precise, but it is still a classification tool rather than a complete description of the game. Use the A-E family map on this page as a guide to neighborhoods, not as a claim that every game is identical.

Yes. The same named opening can sometimes appear under different ECO codes if the move order changes or if the game branches into a different sub-variation. ECO is organised by opening classification, not just by one fixed name.

This is especially common in openings with flexible transpositions, where similar positions can be reached by different paths. Use the lookup tool here as a fast starting point, then compare the nearby family ranges in the volume map.

Yes. Different openings can share the same first few moves and still receive different ECO codes once the position branches into a distinct family. The code becomes clearer only after the opening has declared itself more fully.

This is one reason early crossroads codes such as E00 are so important: they mark a transition before the line settles. Use the quick answer cards and the Volume E breakdown here to see that branching effect in practice.

No. Memorising ECO codes can help you organise opening study, but it does not replace understanding plans, pawn structures, tactical themes and typical middlegames.

A code tells you where you are, not how to play the position well. Use this page to identify the family quickly, then treat the code as a study map rather than the end of the story.

E00 is not just one named opening because it often marks an early branching point after 1.d4 Nf6 2.c4 e6. From there, the game can still develop into several more specific families such as the Catalan, Queen's Indian or Nimzo-Indian.

That makes E00 especially useful for classification, even though it can feel vague to players expecting one neat label. Use the E00 quick answer card on this page and then compare it with the later Volume E families to see how the road splits.

E12 points to the Queen's Indian Defense, while E20 points to the Nimzo-Indian Defense. The key distinction is that E12 follows a route with Nf3 and b6, while E20 reaches the Nimzo with Nc3 and Bb4.

This comparison matters because both openings begin with similar Indian-defense ingredients before they separate into very different strategic families. Use the lookup tool here to compare E12 and E20 side by side, then check the Volume E family map below.

C42 is the Petrov Defense, while C50 is the Italian Game. C42 begins with 1.e4 e5 2.Nf3 Nf6, while C50 follows 1.e4 e5 2.Nf3 Nc6 3.Bc4.

The difference matters because both codes live in Volume C but lead to very different strategic worlds. Use the quick answer cards and the Volume C section on this page to compare where each code sits inside the broader open-game family tree.

The fastest way to find an opening name from an ECO code is to use a code-to-name lookup and then check the broader family range. A code such as E20, E12 or D40 usually identifies the family immediately.

That is exactly what the lookup tool on this page is for. Enter the code in the quick ECO lookup box, then use the jump link and family map to see the larger opening group around it.