---
id: test-parallel
title: "Parallelism and sharding"
---

Playwright Test runs tests in parallel by default, using multiple worker processes.

<!-- TOC -->

## Workers

Each worker process creates a new environment to run tests. By default, Playwright Test reuses the worker as much as it can to make testing faster.

However, test runner will create a new worker when retrying tests, after any test failure, to initialize a new environment, or just to speed up test execution if the worker limit is not reached.

You can control the maximum number of worker processes via [command line](./test-cli.md) or in the [configuration file](./test-configuration.md).

- Run in parallel by default
  ```bash
  npx playwright test
  ```

- Disable parallelization
  ```bash
  npx playwright test --worker 1
  ```

- Control the number of workers
  ```bash
  npx playwright test --worker 4
  ```

- In the configuration file
  ```js
  // playwright.config.js
  module.exports = {
    // Limit the number of workers on CI, use default locally
    workers: process.env.CI ? 2 : undefined,
  };
  ```

  ```ts
  // playwright.config.ts
  import { PlaywrightTestConfig } from 'playwright/test';

  const config: PlaywrightTestConfig = {
    // Limit the number of workers on CI, use default locally
    workers: process.env.CI ? 2 : undefined,
  };
  export default config;
  ```

Each worker process is assigned a unique sequential index that is accessible through the [`workerInfo`](./test-advanced.md#workerinfo) object.

## Shards

Playwright Test can shard a test suite, so that it can be executed on multiple machines. For that,  pass `--shard=x/y` to the command line. For example, to split the suite into three shards, each running one third of the tests:

```bash
npx playwright test --shard=1/3
npx playwright test --shard=2/3
npx playwright test --shard=3/3
```