The Opening Explorer is a chess learning tool, which allows you to study openings move by move. The Opening Explorer contains literally millions of pages, one for each chess position which can be found in the opening. You see the position on the left of the screen, and you select moves from the "move list" on the right side. It can be used in many different ways, as this document will explain.

The Opening Explorer is only free in a limited capacity. You are allowed to only view a few moves deep into opening. However, to see a full featured demo, the "Opening of the Day" on the home page is always 100% enabled. To enable the full power of The Opening Explorer, you must become a Chessgames Premium Member.

That is a graph which represents the results of the move. White = percent that White wins the game, Black = percent that Black wins the game, and Grey = percent that the game is drawn.

Until the possibility of transposition is excluded, it is impossible to say with certainty what opening a position represents. Displayed in the lower right is the list of all openings that the given position might be. You never know for certain which opening the position is, until either a novelity is made, or you have played beyond all transpositional possibilities. When that happens, the list of many possibilities will automatically reduce into one.

The numbers in parentheses can give you a statistical evaluation of which openings are the mostly likely outcomes.

FEN, or Forsyth-Edwards Notation, is a method of representing a chess position in a compact string. A typical FEN code might look like this:

rn1qkb1r/pb1p1ppp/1p2pn2/2p5/2P5/2N2NP1/PP1PPPBP/R1BQK2R w KQkq

We provide this string for compatibility with certain software products which can accept FEN codes. The FEN codes we use are technically not complete, since the en passant information is stripped off of the end. (This is not a bug--we realized during development of the Opening Explorer that ignoring this information conveys distinct advantages when computing transpositions.) For a more detailed description of how FEN words, see the FEN Standard Document from Chessville.com.

On each page of the Opening Explorer, you will find a link which reads "adds notes." This is a feature for opening scholars who want to store notes on certain positions for later reference. To add a note, simply click on "add notes", then fill out the window that pops up. When you revisit the page (or press 'refresh' on your browser) the notes will appear in a large white box.

Notes are 100% private: they are only visible when you are signed-in with your account. Other users cannot see your notes, even if you want them to. Notes can contain Kibitzing Tricks such as links to games, figurine notation, etc.

The Repertoire Explorer is a subset of the Opening Explorer. It allows you to explore the opening moves of a specific player.

It has been said that the best way for a non-professional player to build a strong opening repertoire is to model their opening play after a grandmaster he or she admires. Using this tool, you can do just that.

For professional players, this feature is even more valuable. If you are going to be playing somebody in the database, the Repertoire Explorer is the ultimate preparation tool, as it can be used to learn the specific moves that your opponent is likely to play in various positions.

To activate the Repertoire Explorer, first go to the main page of the player you want to examine. (E.g., type in 'Kasparov' on the main search page.) Then, you will see a graphic that looks like this:

To examine the player's games with the white pieces, click on the white pawn. For the black pieces, click on the black pawn. All normal features of the Opening Explorer work, except that they are limited to the player in question.

Here is an annotated snapshot of the Repertoire Explorer in action:

When the examined player is "on the move" (for example, if you are examining openings with the white pieces and it's White's move) the moves listed are the moves that this player made in that position. When the examined player is "off the move" (for example, if you examining openings with the white pieces and it's Black's move) then the moves shown are the moves that their opponents have played in that position. The win-draw-loss statistics shown in the move list are the results that the player has achieved with each move.

We are developing a feature which does exactly that. For now, you have plug the moves in one at a time.

Not all games in the database are able to be indexed by the Opening Explorer. For example, odds-games, very short draws, Fischerandom games, and other oddities cannot be indexed in terms of opening theory. Furthermore, there is a delay (usually a few days) between when we receive new games and when they are fully indexed into the Opening Explorer.

Due to transpositions, the moves column may contain games that never saw the position shown. The total you see on the left side is the number of games which actually saw the exact position shown, while the totals in the right columns are the games which contain the position that would be created, if that move was played. For example, after 1.f4 e5 (From's Gambit) you will find only a handful of games; but there are thousands of games dealing with the position that results when White goes on to plays 2.e4 (The King's Gambit.)

Not necessarily. Unusual moves may be wrong, but statistically they can be effective due to "shock value." On the other hand, some openings are unpopular at the GM level and yet perfectly good. If you study these unpopular openings you may find lots of examples of GM's crushing weaker opponents who attempt them; but don't conclude that the opening itself is always at fault. You must decide for yourself which move will best challenge your opponents.

Not necessarily. Sometimes a certain line is popular for many years until a bust is discovered, at which point grandmasters stop playing it. However, the net statistics will still show that during most games in the database, the old (inferior) move is made. However, for most of the common openings the top move will almost always be extremely solid and safe.

Click on any move in the displayed line; you will jump directly to that position. If you want to go back to the initial position, click on the "new line" button.

That just means that there wasn't enough room to display the number. You can deduce the missing value by subtracting the other two percentages from 100.