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Configure browser projects once, then choose how much coverage to run
Playwright projects let one test suite run with different browser or device configurations. A typical cross-browser setup defines Chromium, Firefox, and WebKit in playwright.config.ts. Use the same functional tests across projects when behavior should match; add project-specific tests only when a browser or device needs distinct coverage. Projects can also represent device profiles or branded Chrome and Edge channels. See Playwright projects and supported browsers.
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import { defineConfig, devices } from '@playwright/test';
export default defineConfig({
projects: [
{ name: 'chromium', use: { ...devices['Desktop Chrome'] } },
{ name: 'firefox', use: { ...devices['Desktop Firefox'] } },
{ name: 'webkit', use: { ...devices['Desktop Safari'] } },
],
});Run every configured project with npx playwright test. During a browser-specific change, run just that project—for example, npx playwright test --project=webkit. A targeted run speeds local feedback but complements rather than replaces the browser matrix you intend to validate. Project names are the names configured in the file. The CLI reference documents the available command-line options.
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Choose a worker count that your runner and tests can sustain
Playwright runs test files in parallel by default; tests within an individual file run sequentially by default. The worker limit controls concurrent execution, and the TestConfig API documents a default of half the logical CPU cores. You can set a limit in the command, such as npx playwright test --workers=4, or configure it for a run. That example is not a universal recommendation: concurrent browsers also need memory and can compete for CPU. More workers help only when the runner has spare capacity and the suite is safe to run concurrently. See Parallelism and the TestConfig API.
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Use a stable CI baseline before increasing concurrency
Playwright’s CI guidance recommends one worker for reproducibility and stability. Treat that as a starting point, not a benchmark or a rule for every environment. Measure suite duration and failures at the baseline; then increase workers on adequately provisioned agents if reliability remains acceptable. Powerful self-hosted CI may support more parallel work. The right value depends on the suite and runner, so the documentation does not imply a fixed speedup. See Playwright’s CI guidance.
Use fullyParallel when individual tests need to distribute more flexibly
The fullyParallel setting allows individual tests to be distributed more flexibly, including during sharding. Enable that model only after tests are independent of ordering and shared state. The configured worker limit still applies to parallel execution.
Isolate shared data before running tests concurrently
Each Playwright test gets its own browser context, which isolates browser state such as cookies and storage. It does not isolate a shared database record, external service account, or output filename. Give parallel tests unique backend data and file paths, or use worker-scoped fixtures when sharing within one worker is intentional. Tests that rely on side effects from earlier tests are vulnerable to order changes and distribution across workers. See Browser contexts and isolation.
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- Create distinct records or accounts for concurrently running tests rather than having them mutate one shared object.
- Use unique output paths for downloads, screenshots, and generated files.
- Keep intentional per-worker shared setup within a worker-scoped fixture; do not assume it is shared safely across workers or CI jobs.
Shard a large suite across CI machines
Workers increase concurrency on one machine; sharding divides a run into indexed partitions that can execute on separate jobs and machines. For a three-way split, launch jobs with npx playwright test --shard=1/3, npx playwright test --shard=2/3, and npx playwright test --shard=3/3. Each job runs its assigned portion. Playwright’s CI guidance recommends sharding when wider parallelization is needed. See shard CLI options, parallelism and sharding, and CI setup guidance.
Sharding can reduce elapsed time when jobs have access to additional machine capacity, but it adds CI orchestration and does not make a single constrained machine more powerful. Suite balance, job startup and setup costs, available agents, and contention affect the result. Configure report merging and artifact collection to match your CI provider. No fixed runtime reduction can be promised from the documented mechanism alone.
Reduce browser setup and failure-diagnosis overhead
Install only the browsers a run needs
Installing only the browser binaries required by the projects being run reduces download time and disk use. If a job runs Chromium alone, install Chromium rather than every browser; install the additional engines for jobs that need them. In CI, caching browser downloads can avoid repeated downloads. Key the cache to the Playwright version so the cached binaries stay aligned with the installed package. Playwright’s best practices cover browser installation and debugging guidance.
Collect traces on retry rather than for every passing test
The Playwright CI example configures traces on the first retry, and the documentation cautions that tracing every test is performance-heavy. Use retry-based traces to retain useful context for failures without paying the capture cost on every successful test. Open trace artifacts with the Trace Viewer when investigating a failure; keep artifact collection matched to the debugging needs of your CI workflow. See Best Practices.
A practical fast-test workflow
- Define the intended coverage. Add projects for the browser engines and device configurations your product supports.
- Run the matrix. Use
npx playwright testto exercise all configured projects; select one with--project=<name>for focused local iteration. - Establish a CI baseline. Begin with one worker per Playwright’s CI guidance, then measure duration and stability on your actual runner.
- Make concurrent tests independent. Isolate backend records, accounts, and file paths before increasing workers or distributing shards.
- Scale with available capacity. Raise
--workersfor a capable single agent, or use--shard=i/nacross CI jobs when more machines are available. - Trim repeated setup and debug costs. Install and cache only the needed browser binaries, and retain traces on retry rather than for every test.
Troubleshooting slow or flaky cross-browser runs
A higher worker count makes the run slower or unstable
Concurrent browser processes may be saturating CPU or memory, or tests may be racing over shared state. Return to one worker, inspect runner capacity, and isolate shared backend data and output paths before raising the limit again.
One browser project fails while another passes
Run the failing project alone with npx playwright test --project=<name> to narrow local diagnosis. Compare the project configuration and browser-specific behavior, then run the full matrix after the change so a focused pass does not conceal regressions elsewhere.
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Tests pass alone but fail in a full run or on another shard
Look for ordering assumptions or shared external resources: browser contexts isolate cookies and storage, not databases, service accounts, or files. Make the affected test’s data and artifacts unique, then rerun with the intended parallel or sharded setup.
CI spends too long downloading browsers
Check whether the job installs browsers it does not use. Install only the binaries required by its projects and cache downloads with a key tied to the Playwright version.
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Enable retry-based tracing and inspect the trace artifact with Trace Viewer. Capturing traces for every test can impose unnecessary performance cost, especially when most tests pass.
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