How do you troubleshoot a GitLab Runner stuck in "pending"?

A pipeline stuck showing pending almost always means GitLab can't find an available runner that matches what the job is asking for, rather than the runner having crashed mid-job.

1. Check runner availability - In Settings > CI/CD > Runners, confirm at least one runner is online and not paused.
2. Check tags - If the job specifies tags:, confirm a runner registered with those exact tags exists; a mismatch (even a typo) leaves the job unassignable.
3. Check runner scope - A project-specific runner won't pick up jobs from other projects; a group runner needs the project to be inside that group.
4. Check concurrency limits - If every runner is already busy at its configured concurrency limit, new jobs queue instead of starting.
5. Check runner logs - On self-hosted runners, gitlab-runner status and the runner's system logs will show connection or registration errors.

Most "stuck pending" cases resolve once the tag mismatch or offline runner is found; it's rarely a pipeline syntax problem, since GitLab would report a config error separately rather than leave the job pending.