In GitHub Actions, what is the difference between 'jobs' running in sequence versus in parallel?
Select an answer to reveal the explanation.
Short Explanation and Infographic
GitHub Actions is parallel by default — if you define three jobs without any dependencies, all three start at the same time. Use 'needs' to chain jobs together when job B depends on job A finishing first.
Full explanation below image
![Educational infographic showing GitHub Actions job execution models. Left side: Three independent jobs (build, test, lint) running simultaneously with parallel timeline bars. Right side: Sequential jobs using 'needs' keyword showing build → test → deploy pipeline. Display YAML snippet showing 'needs: [build]' configuration. Include timeline showing time savings with parallelism. GitHub Actions orange and blue timeline design. 1024x768 pixels.](/media/github/gh-100/GH-100-q033-infographic.webp)
Full Explanation
In GitHub Actions workflows, jobs run in parallel by default — all jobs defined in a workflow start simultaneously unless dependencies are specified. To enforce sequential execution or define dependencies between jobs, use the 'needs' keyword. For example, 'needs: build' on a 'test' job means the test job won't start until build completes successfully. If the dependency job fails, dependent jobs are skipped by default. Matrix strategies multiply individual job configurations but each matrix combination still runs in parallel (subject to runner availability and concurrency limits). This parallel-by-default design speeds up workflows when jobs are independent.