Checkers endgame tablebase — every position with four pieces or fewer, solved

6,408,836 American checkers (English draughts) positions, each with an exact result and an exact distance to the end. Not an evaluation, not a search: won, lost or drawn, and in how many moves. One 1.8 MB file, a reader in one Python module, no dependencies and no service to call.

Play any of it in the browser at checkersarena.io/checkers-endgame/.

Why this exists

Checkers was solved in 2007 by the Chinook team, who proved that perfect play by both sides is a draw. That proof rests on enormous endgame databases — but those are not something you can download, open and read this afternoon.

Meanwhile every free checkers "solver" on the web is a search engine with a time budget. Search is at its worst exactly where this table is exact: in an ending with a handful of pieces, where the win may be fifty moves away and every move looks the same. The longest win here takes 109 plies. No time-limited search will ever find it.

So: the small end of the game, solved completely, in a form you can actually use.

Quick start

python checkers_endgame.py 2bb8r11r7r

8 .....b.b
7 ........
6 ........
5 r.......
4 ........
3 ........
2 .r......
1 ........
  abcdefgh
  red to move

side to move wins in 55 moves (109 plies)
best move: a5-b6

That is the longest forced win in the whole table: two red men against two black men, and Red wins — in 55 moves of perfect play. Add --line to watch the table play it out.

In code:

from checkers_endgame import Board, Tablebase

tb = Tablebase("endgame4.bin.gz")

# pieces go on the dark squares, where (row + column) is odd
board = Board.from_rows([
    "........",
    "..b.....",
    "........",
    "........",
    "........",
    "..R.....",
    "........",
    "........",
], turn="red")

print(tb.probe(board))       # draw with perfect play
print(tb.best_move(board))   # ((5, 2), (4, 1))  — a move that holds it

A king cannot catch a lone man: drawn. Give Red a second king and the same position becomes a win in four moves. The table knows which, and by how much.

Board.from_code also reads the position codec used in checkersarena.io URLs, so any position you can build on the analysis board can be pasted straight in.

What is in the box

Is it right?

That is the only question that matters for a lookup table, because unlike a search bug, an indexing error never announces itself — it just answers confidently about a different position. VERIFICATION.md has the detail; the short version is four checks that share no reasoning:

1. The index is a bijection. Every position maps to one slot and every slot back to one position, checked across every material signature.
2. Local consistency, exhaustively. Every one of the 6.4 million entries must follow from the entries of its own successors. Run over the whole table, not sampled. If every position satisfies the recursion with well-founded distances, the assignment is the unique solution.
3. An independent prover agrees. A separately written search, sharing no code with the generator, has to reproduce the exact distance.
4. Known endings come out right. King against king is drawn; two kings against one wins in 11 moves; three against one in 7. Two thirds of all king-versus-king placements really are drawn, and two kings beat one from every placement but 34.

And one invariant that needs no reference at all: a game ends when the loser has nothing left, so a win always takes an odd number of plies and a loss an even number. In the shipped file all 2,675,270 winning distances are odd and not one is even. Any drift in the unit of distance would break that immediately.

You can re-run the cross-check yourself:

python verify_reader.py cases.json

400 positions checked
  slots     400/400 agree
  verdicts  400/400 agree
  moves     400/400 agree
  parity    160/160 wins odd, 126/126 losses even

The reader in this repository was written from the format specification rather than translated from the generator, so that check is two implementations agreeing rather than one implementation agreeing with itself.

Why distances and not just win/loss/draw

Three outcomes would be enough to never throw a win away, and not enough to ever finish one. Every move in a won position keeps the win, so a table without distances has no reason to prefer any of them and will shuffle pieces forever. Storing the distance is what makes the table able to actually deliver the 55-move win rather than merely know that it exists.

How it was built

Forwards, not backwards. The obvious way to build a tablebase is retrograde analysis — generate the predecessors of a position, which means writing a reverse move generator that un-captures pieces and un-crowns kings. That is new, untested code at the most delicate point in the whole project.

Instead the successor graph is generated with the same rules engine that validates real games on the live site, and then walked in reverse. No new rule code, and the move generator is the one that has been exercised by every game ever played on the site.

Positions are grouped by material signature so memory stays bounded, and the signatures are solved in an order where each depends only on ones already finished — with one exception: a signature and its mirror depend on each other, because only red-to-move positions are stored, so those two are solved together as a single group.

Citing it

The dataset is archived at CERN and has a permanent DOI, so it stays citable whether or not this repository does:

Checkers Arena (2026). Checkers endgame tablebase: all positions with four pieces or fewer, solved exactly. Zenodo. https://doi.org/10.5281/zenodo.23002848

Use 10.5281/zenodo.23002848 — the concept DOI, which always resolves to the newest version. 10.5281/zenodo.23002849 points at v1.0.0 specifically, which is what you want only if you need to pin the exact bytes you worked with.

CITATION.cff is in the repository, so GitHub's "Cite this repository" button will format it for you in BibTeX or APA.

Limits, stated plainly

• Four pieces, not more. Five-piece positions need roughly thirty times the space and are not here.
• American rules only. No flying kings, captures compulsory, crowning ends the turn. The table says nothing about Brazilian, international or Turkish draughts, which have different rules and different endings.
• No positions mid-capture-chain. A position halfway through a multi-jump is not one a turn can start from, so it has no slot.
• 14% of the file is unused. Piece classes are ranked independently, which leaves gaps where two classes would claim the same square. A denser scheme exists and is considerably easier to get subtly wrong; the gaps hold a constant byte and compress to almost nothing, so the trade was made deliberately.

Licence

The data — endgame4.bin.gz and cases.json — is CC BY 4.0: use it anywhere, including commercially, as long as you credit it. A credit for a dataset is normally a link:

Checkers endgame tablebase by Checkers Arena, licensed under CC BY 4.0.

The code — checkers_endgame.py and verify_reader.py — is MIT, see LICENSE-CODE.