A BuildKit-based builder that turns application source into runnable container images.
Railpack's CLAUDE.md follows a project from language detection through build planning and container execution. It uses mise tasks, explains what integration fixtures prove, and names generated files and unsafe cleanup commands to leave alone.
├── · imports images/debian/runtime/Dockerfile, mise.toml, docs/src/content/docs/guides/developing-locally.md ├── ├── docs │ └── src │ └── content │ └── docs │ └── guides │ └── ├── examples │ └── tanstack-latest │ └── ├── images │ └── debian │ └── runtime │ └── └──
01 / Verification by change type
The integration-test section limits build-only fixtures because they skip output and other assertions. It directs server projects toward HTTP checks, making the required evidence match the application behavior.
Source excerpt starting at line 72.* In `test.json` we should avoid using `justBuild` for all but the most simple projects. `justBuild` does not test `expectedOutput` or any other assertions.
02 / Behavioral framing
Mise settings belong in a generated TOML file instead of environment variables. The guide gives user override behavior as the reason for choosing that configuration channel.
Source excerpt starting at line 30.- When configuring Mise settings, prefer TOML settings in the generated `mise.toml` (via `AddMiseSetting`) over environment variables, so users can override defaults with their own `mise.toml`.
03 / Hard prohibitions
The guide forbids broad Docker pruning even when the cache behaves unexpectedly. A commonly suggested cleanup command becomes an explicit boundary.
Source excerpt starting at line 42.- Do not worry about docker cache, etc. Never run `docker system prune` or other similar commands.
04 / Generated file guards
The test description separates hand-authored test and service configuration from generated size data. It explicitly forbids creating or editing that generated record manually.
Source excerpt starting at line 66.* The `size.json` is auto-generated and should never be manually created or updated.
These instructions explain how to work in Railpack. Modem shows your agents what customers said, who is affected, and what changed.
