Playwright

Playwright is the best fit when you need chaos from the first page load. The adapter registers Chaos Maker as an init script before page.goto().

npm install @chaos-maker/core @chaos-maker/playwright

The fastest start is a named preset - drop a scenario into the config and run:

import { test, expect } from '@playwright/test';
import { injectChaos } from '@chaos-maker/playwright';

test('checkout works under degraded mobile network', async ({ page }) => {
  await injectChaos(page, { presets: ['mobile-3g', 'checkout-degraded'], seed: 42 });
  await page.goto('/checkout');
  await expect(page.locator('[data-testid="checkout-form"]')).toBeVisible();
});

See the Presets catalog for the full list. When several tests should share the same named scenario, wrap it into a scenario profile - the one built-in demo profile composes both presets above into a single name:

await injectChaos(page, { profile: 'mobile-checkout', seed: 42 });

Pass profileOverrides alongside profile to tune one parameter for this call without forking the profile. When you need precise control, drop down to explicit rules:

import { test, expect } from '@playwright/test';
import { injectChaos, getChaosLog, getChaosSeed } from '@chaos-maker/playwright';

test('shows error state when the API fails', async ({ page }) => {
  await injectChaos(page, {
    seed: 42,
    network: {
      failures: [{ urlPattern: '/api/orders', statusCode: 503, probability: 1 }],
    },
  });

  await page.goto('/orders');
  await expect(page.locator('[data-testid="error-state"]')).toBeVisible();

  const log = await getChaosLog(page);
  expect(log.some((event) => event.type === 'network:failure' && event.applied)).toBe(true);
  console.info('Chaos seed:', await getChaosSeed(page));
});

Log the replay seed only when a test fails:

import { formatSeedReproduction, getChaosSeed } from '@chaos-maker/playwright';

test.afterEach(async ({ page }, testInfo) => {
  if (testInfo.status !== testInfo.expectedStatus) {
    console.error(formatSeedReproduction(await getChaosSeed(page)));
  }
});

Trace integration

Pass testInfo with tracing enabled to annotate Playwright traces and attach the chaos log.

await injectChaos(page, config, { tracing: true, testInfo });

The fixture entry point can also wire tracing automatically for suites that prefer shared setup.

Playwright

Trace integration

Next steps