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Validate Only What Changed

· 2 min read
Erik Osterman
Erik Osterman
Founder @ Cloud Posse

Large repositories often have validation rules that are useful but expensive or noisy to run across every file on every pull request. That makes it tempting to skip validation exactly when a focused signal would be most helpful.

Atmos can now validate the files affected by a change, so pull requests get actionable feedback without rechecking unrelated project inputs.

The Problem​

Configuration schema checks, stack validation, formatting rules, and workflow linting protect different parts of a project. Running every check over an entire repository can obscure the result that matters to the change under review.

The Fix​

Add --affected to the project-wide validator or to an individual validator. Atmos compares the current worktree with the Git merge-base, including local uncommitted and untracked files. In GitHub Actions, it reads the pull request base SHA automatically.

atmos validate --affected --format rich
atmos validate config --affected --base origin/main
atmos config validate --affected --base origin/main
atmos validate stacks --affected --base origin/main
atmos stack validate --affected --base origin/main
atmos validate editorconfig --affected --base origin/main
atmos validate ci --affected --base origin/main

Schema and EditorConfig checks validate changed inputs directly. Changes to a schema or rule configuration expand validation to the relevant full set. Stack validation runs whenever stack or Atmos configuration inputs change, preserving import and duplicate-component checks. Workflow validation sends only changed workflows to actionlint unless its configuration changes.

How to Use It​

Use the new Validation (affected) GitHub Actions job as a model for a project workflow. Check out enough Git history for the merge-base, then run the command with rich output:

- uses: actions/checkout@v6
  with:
    fetch-depth: 0
- run: atmos validate --affected --format rich

Get Involved​

Try affected validation in your pull request workflow and share feedback through GitHub issues.