[tanmay001]

Playwright's parallelism model has three layers. Most teams configure exactly one and wonder why CI is slow or flaky after bumping workers.

The short version: Layer 1 (file-level) is already running by default. Layer 2 (test-level) is what fullyParallel actually controls, and it's widely misunderstood.

Most teams assume it makes browser projects run simultaneously. It doesn't. It changes the scheduler's unit of work from files to individual tests.

Layer 3 is sharding across machines, which you shouldn't reach for until layers 1 and 2 are properly tuned.

The article covers how workers map to browser processes and why overprovisioning them on low-core CI runners causes the timeouts, what fullyParallel does and doesn't do,per-file execution modes (parallel, serial, default) and how beforeAll behaves differently in each, and three isolation patterns that hold up under parallel runs without needing complex fixture setups. https://testdino.com/blog/playwright-parallel-execution/