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Puppeteer’s CSS coverage API documents one option: resetOnNavigation. It defaults to true, resetting coverage on each navigation. Set it to false to disable that automatic reset, but do not treat the setting as a guarantee that coverage will persist across every navigation. These details are in the Puppeteer v25.12.0 API reference.
What CSS coverage options does Puppeteer support?
In the v25.12.0 API reference, CSS coverage has one optional setting, resetOnNavigation. Its default is true. When enabled, coverage resets on each navigation; set it to false to turn off that automatic reset behavior.
This is the full CSS-specific option set documented in that reference. Settings such as includeRawScriptCoverage, reportAnonymousScripts, and useBlockCoverage apply to JavaScript coverage, not CSS coverage.
Choose the navigation scope deliberately
- Keep the default when you want results scoped to each navigation.
- Use
falsewhen you want to disable automatic resets while exercising a multi-navigation flow. The reference does not guarantee that coverage will persist across navigations, so verify the behavior that matters in your own flow.
How to collect CSS coverage
Start collection through the page’s coverage object, exercise the page states you care about, and stop collection to receive stylesheet reports.
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await page.coverage.startCSSCoverage({ resetOnNavigation: false });
// Exercise the pages and states you want represented.
await page.goto('https://example.com/next-page');
const cssCoverage = await page.coverage.stopCSSCoverage();
console.log(cssCoverage);To use the default reset behavior, omit the options object or pass { resetOnNavigation: true }. The call sequence is documented by the startCSSCoverage API and the stopCSSCoverage API.
What the returned reports mean
stopCSSCoverage() resolves to an array of reports for stylesheets. Puppeteer’s official example derives observed used-byte totals by summing range.end - range.start - 1 for each range, then compares that with the stylesheet text length to compute a percentage. Such a percentage describes what the exercised run observed; it does not establish that the remaining CSS is universally unused.
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Important blind spot: injected style tags
Puppeteer’s Coverage documentation states: “CSS Coverage doesn’t include dynamically injected style tags without sourceURLs.” If your application injects styles at runtime, coverage may omit those blocks unless they have source URLs. Exercise the relevant pages and states, and account for injected styles before removing CSS based on a report.
Troubleshooting CSS coverage
- Results reset after navigation: This is the default when
resetOnNavigationis omitted. Set it tofalseto disable the automatic reset, then test whether the resulting reports cover your flow as intended. - Expected injected CSS is missing: Dynamically injected style tags without sourceURLs are not included. Do not interpret their absence as proof the styles are unused.
- Coverage appears to show CSS as unused: The report reflects the page states and interactions exercised during collection. Visit the states that use the styles before using the result to make cleanup decisions.
- You are looking for other CSS settings: The v25.12.0 reference documents only
resetOnNavigationfor CSS coverage. The named optionsincludeRawScriptCoverage,reportAnonymousScripts, anduseBlockCoverageare JavaScript coverage options.
Or skip the browser setup
If you need screenshots of pages rather than stylesheet coverage, ScreenshotNeo offers a one-request screenshot API. Its documented request can return a screenshot or PDF; this is a separate task from collecting Puppeteer CSS coverage.
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