# Hexodic move-legality checker.

> Build a position, propose a turn, and let the rules engine rule on it step by step.

Enter a complete Hexodic turn — Project, Shape and Echo — and the canonical rules engine says whether each step is legal, and what the turn captures or wins if it is played.

Canonical HTML: https://hexodic.com/move-legality-checker
Site index for agents: https://hexodic.com/llms.txt

## Is this Hexodic turn legal?

The Hexodic move-legality checker answers that question by comparing your proposed turn with the rules engine's own list of legal actions, one step at a time: first the Project, then the Shape that follows it, then the Echo. A Hexodic turn is legal only when all three steps are legal in order, because each step changes what the next step may do.

## How to use the checker

1. **Set the position.** Leave the replay code empty for the opening position, or paste a replay code from the [branching-factor explorer](/branching-factor-explorer). A **replay code** is a dot-separated list of turn numbers taken from the engine's ordered list of legal turns.
2. **Describe the turn.** Choose Place or Move with its cells, a Shape (raise, lower or skip) with its cell, and an Echo choice. Selecting a board cell fills in the destination.
3. **Check it.** The checker reports each step as legal or illegal, with how many options the engine allows at that step.
4. **Continue.** When a turn is legal you can play it, and the position advances so you can check the next turn.

## What the checker computes

- **Staged legality** from the engine's legal Project, Shape and Echo lists, confirmed by the engine's whole-turn legality check.
- **Capture flag for moves** — whether a move captures the stone it lands on is decided by the engine, not by you.
- **Result of a legal turn** — the cells captured and, if the turn ends the game, the win condition: Network, Takeover or Strangle.
- **Position summary** — reserve, Echo charges, captures and whether each player's Network or Takeover condition is complete, as reported by the engine's win checks.

## What the checker cannot determine

The Hexodic move-legality checker does not explain *why* an illegal step is illegal beyond reporting that the engine does not list it. The checker cannot see a game's history, so a repetition loss is never reported. The checker also does not judge whether a legal turn is a good turn.

Learn the turn structure in [how Hexodic is played](/how-it-works), or read about [deterministic strategy games](/deterministic-strategy-game). Then [get the Hexodic app](/download).

*Reviewed 2026-09-15.*

## Where to go next

- [Project](https://hexodic.com/rules/project) — The first step of a turn: place a stone, or move one.
- [Strategy](https://hexodic.com/strategy) — The principles that follow from the rules, not from habit.
- [How it was measured](https://hexodic.com/how-hexodic-was-measured) — The evidence behind every published number, and the method.

## Questions this page answers

- How do I check if a move is legal in Hexodic?
- Can I check Hexodic win conditions for a position?