The Gammon.ai user guide

Install, sign in and start

Everything in Gammon.ai runs on your own computer. The Galaxy engine is installed with the app, so analysis keeps working without an internet connection once you have signed in. Your matches, saved positions and profiles are stored on your computer too.

Install

• Mac: needs macOS 12 or later on an Apple Silicon Mac (M1 or newer). Open the download and drag Gammon.ai into your Applications folder.
• Windows: needs Windows 10 or 11, 64-bit. Run the installer. It installs for your user account only, so no administrator rights are needed. Afterwards, double-clicking a .mat file opens it in Gammon.ai.

Sign in with Backgammon Galaxy

1. Click Sign in with Backgammon Galaxy.
2. Your web browser opens the Galaxy login page. Log in as you usually do.
3. Go back to Gammon.ai. It checks your membership and opens the home screen.

There is no separate Gammon.ai password. You can keep using the app offline for up to 48 hours after your last membership check; going online renews it automatically.

Star and Star Pro

Gammon.ai is included with a Backgammon Galaxy Star or Star Pro membership. Your membership decides which analysis depths you can use.

Anything above your membership shows a small lock. Click it to see what it needs and a link to the membership page.

The home screen and main menu

The home screen has a tile for each tool, plus Join live session. The main menu runs down the left side; the arrow at the top switches between a slim strip of icons and a full menu with labels.

Lower in the menu are links to Trackgammon (automatic transcription of live matches), Gammon.gg (live tournaments) and Backgammon Galaxy (play online), then Live session and Log out. The version number at the bottom opens About, which also tells you when an update is available.

How deep the engine thinks

Every analysis in the app is done by the Galaxy engine. The analysis level sets how hard it thinks: higher levels are stronger and slower. You choose the level on the slider in the analysis panel.

The horizon is how far ahead each rollout game sees: the number of rolls played before the game is cut off (the truncation point), plus the 1-ply evaluation made at that point. R4 has no horizon, because every game is played to the end.

Opening book

For the first two rolls of a game, Galaxy uses a built-in opening book that has already been rolled out, for money play and for match scores up to 7-away. Plays that come from the book show rollout numbers straight away, even when your slider is set lower, and are labelled Book, which ranks above R4.

Match analysis presets

Analyze Match, Batch Analysis and Transcription let you pick a preset instead of setting every level by hand. Some presets run a 2nd pass, where the close decisions are rolled out after the first look.

Move filter

Before a 2P or 3P search, the engine looks at every legal play at 1P. The move filter decides which of those plays go on to the deeper search: at most a set number of plays, and only plays within a set equity of the best one. The best play always goes through. Wider filters are slower but less likely to miss an unusual play.

• The same filter is used at 2P and 3P. It has no effect at 1P, where every play is already evaluated.
• When the best play leads the second best by more than the window, the decision is clear: no play goes deeper and the 1P result stands. Off always searches deeper.
• In match play the window is converted to match-winning chances.
• For cube decisions no plays are filtered, but the window decides when a cube decision is already clear at 1P.
• In rollouts the filter picks which plays are rolled out: the same limits as above (at least 2 plays), then a second cut to at most 3 close plays within 0.02 (Tiny), 0.03 (Narrow), 0.04 (Normal), 0.08 (Large) or 0.11 (Huge). Off rolls out every legal play.

You choose the filter in Play vs AI, in the match analysis settings and in the rollout settings; all of them start on Normal. The analysis panel uses a fixed filter: Normal at 2P, and at 3P Narrow in Play vs AI and match review, Normal in Set Up Position.

Reading and deepening the engine's answer

The same analysis panel sits next to the board in Play, Analyze Match, Transcription, Set Up Position and the Library. It lists the engine's candidate plays, or the cube actions, best first.

• Get the engine's plays: press H or click Analyze.
• Preview a play: click a row and the board shows it. The Arrows / Final position switch chooses between arrows for each checker and the position after the play.
• Go deeper on some plays: click one or more rows to mark them, move the slider to a deeper level, then click Analyze. Only the marked plays are analysed again, which is much faster than redoing the whole list. Rollouts show a progress bar with Interrupt to stop early and keep what is done.
• Cube decisions analyse again by themselves when you move the slider.
• Make a play: double-click a row to play it on the board.

Each row shows the equity and how much it loses to the best play. Under the list are the winning chances: wins, gammons and backgammons for each side.

Panel settings

The gear beside the slider has: Show as MWC (match-winning chances instead of equity, in match play), Show winning chances on every move, Count hitting shots (how many rolls hit your blots, optionally as combinations out of 36) and Custom Rollout.

Right-click a move

Right-click any move in the move log for Set Flag, Clear analysis, Save position to the Library, Open in Set Up Position, Dice Distribution, Cube theory, Match equity table, and, in Transcription, Replay from here.

The most reliable answer

A rollout plays a position out hundreds of times with the engine on both sides and averages the results. It is the most reliable answer the app can give, and the slowest. Rollouts are repeatable: the same rollout gives the same result every time.

All of them switch to exact bear-off tables near the end of the game.

Custom rollouts

• Trials: the number of games, always a multiple of 36 so every first roll comes up equally often.
• Checker play and cube levels for each player, or the same for both.
• Truncation: stop each game after a number of moves and let the engine estimate, or play every game to the end.
• Stopping: stop early once the result is clear enough.

Save as… keeps a setup under your own name in the presets list. You can also overwrite R1 to R4 with your own settings; Reset brings back the originals.

Play the Galaxy engine

Play a match of 1 to 17 points, or a money game. Before you start you choose the engine's strength for checker play and cube decisions (lower levels make a softer opponent), the move filter, whether hints are allowed, whether to show your error rate as you play, and the rules: Crawford for matches, Jacoby, beavers and a cube limit for money games. Click Start Match. Earlier games are listed under Your matches vs AI and can be resumed.

During the game

• Click the dice or press Space to roll. Click the cube or Double to double. When the engine doubles, answer Take or Pass, or Beaver in money games with beavers.
• Drag or click checkers, then click the dice to finish your move.
• With hints on, press H to see the engine's view.
• Resign offers a single, gammon or backgammon. The engine accepts any resignation.
• Download .mat saves the match; Analyse sends it straight to Analyze Match. Log View / Chart View switches between the moves and a live match-winning-chances chart.

Play from position

Practise one position again and again. Start it from Play from Position in the lobby (paste an XGID) or from Set Up Position. Every attempt starts from the same position with the same dice, cube, score and rules, and Gammon.ai scores your results like a chouette or a manual rollout: Session results shows how many points you won per game, cube included.

Find every error in a match

Analyse a match you played on Backgammon Galaxy, in another program or over the board.

Import

Drop match files onto the page or click to pick them. Gammon.ai reads .mat, .txt, .sgf (GNU Backgammon) and .xg (eXtreme Gammon) files. If a match did not start from the opening position, paste a GNU Position ID or XGID under Starting position before importing. Imported matches can be filtered by date, source and length; tick several and choose Batch Analyze to do them together.

Choose how deep

Click Analyze and pick a preset (see Analysis levels). You can analyse each player at a different level, and open the 1st-pass and 2nd-pass details to set everything by hand.

Review

• Step through decisions with ↑ ↓ and between games with ← →.
• Mistakes and blunders are marked in the log. Flag any move to find it again later.
• Match Stats shows each player's error rate, Galaxy PR, blunders, cube errors (missed doubles, wrong takes and passes) and luck. From there, Add to profile saves the result, and Archive to Blunder Database saves the positions before each mistake into the Library.
• Chart view opens Match Review: each player's match-winning chances move by move, with the key moments marked. Click a point to jump to that move.
• Download as .mat (the match only) or .gai (the match with its analysis, to open again in Gammon.ai).

Record a match as it is played

Transcription records a match move by move while it is played, for example over the board at a club or tournament. The engine can analyse each move as you go, and everything is saved the moment you enter it, so closing the app never loses a match.

Start a match

Create a new match and fill in the form: player names and flags, match length or single game, board, analysis level and notes. Options include manual dice, pip count, bear-off side, show error rate, cube limit and beavers.

Enter moves with the keyboard

1–6

type a die

R

random roll

Enter Space

commit the move

Backspace

undo the last entry

D

double

T

take (when doubled), otherwise take back

P

pass (when doubled)

H

hint: the engine's plays

I

add an illegal move, as it really happened

⌘C / Ctrl+C

copy the position ID

↑ ↓ ← →

step through moves and games

The buttons beside the board do the same, plus Finish game, where the engine plays the rest of the game out. Spotted an entry mistake several moves back? Right-click that move and choose Replay from here. It deletes that move and everything after it, so use it with care.

When the match is over, click Analyze for a full match analysis.

Build any position and analyse it

• Click points to place checkers, and drag the cube to set its value and owner.
• Or paste an XGID or GNU ID with ⌘V / Ctrl+V. Copy XGID copies the current one.
• The tool strip has Settings, Clear, Reset, Cube action / Checker play, Flip colours and Direction.
• Settings sets match or single game, match length, each player's score, Jacoby and Crawford.

Pick a level beside Analyze (2P by default) and click it. In the results, move the slider and analyse again to go deeper. Save pos stores the position in a Library folder, and Play from Position starts practice games from it.

Look deeper into one position

These open from the right-click menu on a move, or from the study menu in Set Up Position.

Dice distribution

Shows what each of the 36 rolls does. For a checker play it compares your play with another, roll by roll, one or two rolls ahead. For a cube decision it shows which rolls make the position too good or lose your market. The Swing rolls view highlights the rolls that matter most.

Cube theory

The key cube points for both players: doubling point, take point, cash point, too-good point, and beaver and raccoon points where allowed. Change the score, cube or gammon rates to see how the points move, without changing the match.

Match equity table

Your chance of winning the match from any score, with the current score highlighted.

Match score table

The same decision analysed at every match score, in one grid: blue where doubling or taking is right, red where it is wrong, and for checker plays, where the best play changes. Large tables run in the background and can be stopped at any time, keeping what is done.

Your own position collection

Saved positions

• Create folders and save positions into them from Set Up Position or the move log.
• Open a position in Set Up Position, rename, move or duplicate it, or delete it.
• Import XG position files (.xgp) or a Library folder file (.gai). Download exports a folder as .gai to share with a friend.

Blunder Database

Your own mistakes from analysed matches, sorted by position type. Fill it with Archive to Blunder Database after a match analysis, or with Archive mistakes in Batch Analysis.

Position Quiz and Blunder Quiz

Both quizzes show one position at a time: make the move, double or roll, take or pass. You see whether you were right, how much your choice lost and whether it was a close decision. Position Quiz uses the folders you tick; Blunder Quiz replays your own archived mistakes.

Follow your game over time

A profile collects analysed matches for one player. Create one with New Profile, or straight from Match Stats › Add to profile. Group matches into events such as a tournament or a league, and use Link profiles if you play under several names.

• Error Rate (ER) and Galaxy PR overall, for checker play and for cube action.
• A radar chart of your error rate by position type.
• Cube detail: missed doubles, correct and wrong doubles, takes and passes.
• Luck per match compared with your opponents, and dice averages.
• Wins, losses and the list of matches.

Galaxy PR: a skill-adjusted error rate

The Galaxy Performance Rate (PR) weighs each decision by how difficult it is. That makes it different from Galaxy's Error Rate (ER) and from XG's Performance Rating, which is also called PR. Lower is better, and each PR comes with a level of play:

Analyse a whole tournament at once

1. Drop up to 1,000 match files onto the page (.mat, .txt or .sgf), or add matches already in Analyze Match.
2. Link each player to a profile, or leave them unsaved.
3. Pick an analysis preset, and tick Archive mistakes to send everyone's mistakes to the Blunder Database.
4. Click Analyze Now, or Queue to add to a batch that is already running.

Progress shows as done / total. When it finishes, download all matches as .gai (with analysis) or .mat.

Follow a match or position together

Share a Transcription or Set Up Position screen with other Gammon.ai users: follow a club match together, teach a position, or keep a broadcast crew in sync.

Host

Open Live session in the main menu, or from Settings on the screen you want to share, choose what guests may do and click Start. You get a 4-digit code to give your guests.

• View only: guests follow the match and browse it freely. They can run deeper analysis on their own computer and share it with everyone, but never change the match.
• Interact (Set Up Position): everyone can edit the position and share analysis.

You can see and remove guests, and Stop live session ends it for everyone.

Join

Click Join live session on the home screen and type the code.

Explanations in plain language

Click the Coach button (the light bulb) in the analysis panel for an explanation in words of why the best play is best, or why a cube decision is right or wrong. Coach needs an internet connection.

Make it yours

• Board themes: Neptune, Nebula, Singularity and Winter, from the board menu.
• Custom board: upload your own image, adjust saturation and brightness, and save it under a name.
• Full screen or windowed, and arrows to hide the main menu or shrink the moves and analysis side.
• Strategy note: a notepad for your own notes on a position.

Terms used in the app

Equity

The expected result of the position in points per game, counting gammons and the cube. Positive is good for you.

MWC

Match-winning chances: your chance of winning the match, in percent.

ER

Error rate: the equity you lost to the engine's best choices, per decision.

Galaxy PR

Galaxy Performance Rate: your errors weighted by how difficult each decision was. Lower is better.

Ply

How many rolls ahead the engine looks. 1-ply is its direct judgement; 3-ply looks two rolls further.

Rollout

Playing a position out many times and averaging the results.

Horizon

How far ahead a rollout game sees: the rolls played before it is cut off (the truncation point), plus the evaluation made there.

Truncation

Stopping each rollout game early and letting the engine estimate the rest.

XGID / GNU ID

A short text code for a position, its dice, cube and score. Paste one into Set Up Position to open it.

DMP

Double match point: both players one point from winning.