Engine Analysis

A match file from eXtreme Gammon or GNU Backgammon already carries every candidate, equity, and luck figure the analyzer computed, and BackgammonDB shows those as they are. A .mat or .txt file carries nothing, and an XG or GNU file can hold decisions the analyzer skipped. For those, the review screen asks GNU Backgammon, running on our server, and shows the answer in the same candidate strip.

The request is the position and its match context — the board, the dice, the cube, the score, and the move played. Nothing else leaves your browser: not the match file, not the rest of your library, not your notes. The one exception is Analyze match (below), which sends the moves of that match and both player names for that one analysis.

What you see on an unanalyzed decision

Land on a decision the file never scored and the candidate strip shows a placeholder in its own layout. Once the cursor rests on the action for a moment, a Quick evaluation replaces it: the ranked candidates, their equities, and the win-chance breakdown, exactly as an analyzed decision reads. Nothing was clicked, and nothing was written — this ambient result is for the current session only. Step away and back and it is fetched again.

The engine bar

Above the candidate list sits the engine bar: a badge naming the quality of the result on screen, and the tier chips beside it.

Badge	Meaning	Hover for
◔ Quick	gnubg 1-ply — the ambient default	gnubg 1-ply · comparable to XG 2-ply
◑ Smart	gnubg 2-ply	gnubg 2-ply · comparable to XG 3-ply
⚡ Book	an opening position answered from the precomputed opening book	Opening book · precomputed gnubg 3-ply

The tooltips carry the honest GNU Backgammon plies. gnubg and XG count plies differently — gnubg's 2-ply is close to what XG calls 3-ply — so the tiers are named rather than numbered.

The Deep chip is shown disabled. Its tooltip says why: deep analysis is coming with accounts, and the engine evaluates up to Smart today.

A Book result has no chips at all. The opening book already holds the deepest answer the engine can give, so there is no deeper tier to ask for.

Keeping a result

Click Quick or Smart in the engine bar and the result is written onto the stored match. From then on it behaves like analysis that came with the file:

• the action list shows the error marker and the equity loss for that decision,
• the played move's arrow is colored by the size of the error,
• the positions browser and the stat sheets include it,
• and it survives a reload — every reader of that match sees it.

A deeper result upgrades a stored one in place; a shallower result never downgrades it. Click Smart on a decision that already holds a Quick result and the Smart numbers replace it. Click Quick on a decision that already holds Smart and the display follows your click for this session, but the stored record keeps Smart.

Whatever you click, the display follows the click on the current action. Step away and back and the best-known result shows.

Analyzing the whole match

A match that carries no analysis — a .mat or .txt import — can be analyzed as a whole. Each time such a match opens in review, a dialog asks Analyze this match? and names the depth it will use: Analyze starts it, and Not now closes it until the next time the match opens. The same action lives in Match details (click the scoreline): Analyze match for an unanalyzed match, with a Quick / Smart choice where Smart is on offer, and Re-analyze at Smart for a match this sweep analyzed at Quick.

GNU Backgammon evaluates every decision at the chosen depth. The analysis sends the moves of the match and both player names to our server, one game at a time; nothing else leaves your browser. This is the one exception to the single-position rule above. The server returns the analysis and keeps no copy of the match.

While it runs, the dialog stays open and shows a progress bar counting the games. Keep reviewing hides it: the sweep continues, the button in Match details counts the games meanwhile, and the dialog returns on its own when the sweep finishes. It then shows each player's PR with its level and the checker and cube PR split, and offers two exits: View full match analysis opens the match stats sheet, and Review match returns to the board. Every decision now carries a Quick result (or Smart, if that was the choice), the opening decisions carry the Book answer at 3-ply, the error markers and colored arrows appear in the action list, and the header names the depth: Analyzed by GNU Backgammon (1-ply). A decision you had already evaluated by hand at Smart keeps its Smart result; the whole-match pass never replaces a deeper stored result with a shallower one.

Why the match still has no PR

A match no engine has analyzed as a whole keeps a PR of "—" — in the match header, the library list, the dashboard, library statistics, and the match stats sheet — however many positions you evaluate by hand. The error counts and the equity-lost figures still show, because they are true of the decisions that were evaluated. A PR built from a handful of hand-picked positions would not be: the positions you chose to evaluate are, by definition, not a fair sample of the match. Analyze the whole match and the PR appears.

Files that already carry analysis

On a decision the file scored, the file's numbers win and the engine bar does not appear. There is nothing to evaluate: you are looking at eXtreme Gammon's or GNU Backgammon's own result, at whatever depth the file recorded, and BackgammonDB never replaces it. To try our engine against the file's numbers, hand the position to the analyzer (below), where both sit side by side.

When the engine is unavailable

If the server cannot be reached, the strip shows Analysis unavailable with a Retry chip in place of the ambient result. An explicit chip click that fails shows a short error message instead. The match itself is unaffected — the file's own analysis is stored in your browser and does not depend on the engine.

Open in the analyzer

The pencil chip in the action row under the candidate list — Open this position in the analyzer — carries the position, its match context, and whatever analysis is on screen to Create a Position. There you can move checkers, change the dice or the score, and watch the evaluation follow. A position from an analyzed match arrives with the file's own numbers already showing, badged as the file's. A position from a match our engine analyzed arrives badged with its tier — Quick, or Book for an opening decision.