CircleCI
Cloud-native CI/CD platform with fast parallel builds, Docker layer caching, and cache-based workflows supporting GitHub, GitLab, and Bitbucket repos.
Best for small teams who need fast parallel CI pipelines with Docker caching and multiple OS support.
Use Cases
Free Tier
6,000 credits/month, Linux/Windows runners, 1 concurrent job
How to Maximize the Free Tier
CircleCI's free tier gives you 6,000 credits/month — each credit roughly equals 1 minute of a single-core Linux runner. To maximize them: (1) Enable caching aggressively — dependency layer caching saves credits on every rerun. (2) Use Docker layer caching to avoid rebuilding images from scratch. (3) Keep test parallelization to 1–2 containers max — more containers eats credits faster. (4) Use path-filtering or conditional workflows to skip jobs on docs-only changes. Watch your credit dashboard weekly — a single full rebuild with no caching can burn 50+ credits.
Getting Started
Sign up at circleci.com with GitHub/GitLab/Bitbucket → authorize repo access → select a project → add .circleci/config.yml → define jobs (checkout, restore_cache, run tests, save_cache) → commit → pipeline runs automatically on every push.
Pros
- Parallel builds: Run tests and jobs in parallel across separate containers for faster feedback on every push
- Docker support: First-class Docker support with layer caching — spin up any custom image without extra config
- Generous credits: 6,000 credits/month is a solid free tier for small teams and open-source side projects
Cons
- Credit burn rate: Credits vanish fast with parallel runs or Windows runners — 6,000 can be exhausted in a few days of heavy use
- Single concurrency: Only 1 concurrent job on the free tier — pushes queue up if another build is still running
- No SSH debugging: No SSH access to runners on free tier — troubleshooting failures requires adding debug steps to config