Packages and Version Resolution

Railpack providers will analyze the app and determine fuzzy versions of executables to install. Versions like 3.13, or 22. The version resolution step will resolve those fuzzy versions into the latest valid version that exists.

Mise is used for the package resolution using the mise latest package@version command. Mise is also used for (most) package installations in the builds as well. However, this is not a requirement of Railpack and alternative installation methods are possible (for example PHP will use Mise to resolve a valid version and then start from a PHP base image). Railpack enables Mise paranoid mode for stricter security validation.

For more information on how Railpack utilizes Mise and our philosophy on tool defaults, see the Mise Configuration guide.

Semver constraints from app manifests

Manifest constraints (for example engines.pnpm) are not resolved with npm-style semver. Caret (^) and range (>=, <) notation are simplified to the major version only (^10.34.0 → 10) before Mise picks a release. This is done because Mise does not support compound version constraints right now. Use an exact version or mise.toml to pin. See also minimum_release_age.

Platforms can preserve previously resolved defaults between builds. See Package Version Resolution for the platform integration workflow.