# `once toolchain`

Inspect the project toolchain contract.

## Synopsis

```text
once toolchain <SUBCOMMAND>
```

## Description

Reports the toolchains a project pins (Rust, Swift, mise) and the resolved versions Once will use when running actions from script adapters or graph target kinds. Pair with `once query schema` when debugging "why did the cache miss?" questions where the toolchain identity is suspect.

## Subcommands

- [`once toolchain inspect`](/reference/cli/toolchain/inspect)