Once makes project scripts cacheable, observable, and remotely executable. Declare the inputs, outputs, environment, and runtime contract once, then reuse the result locally, in CI, or on a compute provider.

Describe a script with # once annotations:

#!/usr/bin/env bash
# once input "../assets/**/*"
# once output "../dist/"
# once cwd ".."

npm run build-assets

Run it through the cache:

once exec -- bash scripts/build-assets.sh
once exec --remote --compute microsandbox -- bash scripts/build-assets.sh

Scripts can also run directly with a Once shebang:

#!/usr/bin/env -S once exec -- bash

Read the documentation at once.tuist.dev.

Use the once crate when embedding Once in Rust applications:

[dependencies]
once = { git = "https://github.com/tuist/once" }

Release builds also publish Once.xcframework.zip for Apple platforms. The framework exposes a small C ABI that Swift and Objective-C can call, with JSON requests and responses for cache access.

MIT.