Google released Lighthouse 13 on 10 October 2025 and said it would reach PageSpeed Insights within the following week. The release retired many long-standing performance audits and replaced them with consolidated "insights". Releases through 2026 have since added a Baseline compatibility audit and an experimental Agentic Browsing category. Anyone in the UK who runs a website audit, compares old reports or sends PageSpeed results to clients will see different audit names, even though the performance score is calculated the same way.
Key takeaways
- Lighthouse 13, released on 10 October 2025, replaced many performance audits with consolidated insights.
- Performance scoring did not change, so a score drop around October 2025 has other causes.
- Update audit templates and client reports to map old audit names, such as Defer offscreen images, to the new insights.
- The experimental Agentic Browsing category is not a ranking factor, and Google Search does not use llms.txt files.
What happened
Lighthouse 13: audits become insights
Google's Chrome team had already merged Lighthouse's performance audits with the insights in Chrome DevTools' Performance panel. Lighthouse 12 made the insights view the default, and Lighthouse 13 removed the old audits from both the report and the JSON output. Google said Lighthouse 13 would reach Chrome stable in Chrome 143.
Most importantly, performance scoring did not change. The score is still based on metrics, not audits, and the change affected only non-scored audits.
Some of the main consolidations:
| New insight | Replaces |
|---|---|
| Document request latency | Avoid redirects, server response time, enable text compression |
| Improve image delivery | Modern image formats, optimised images, responsive images, efficient animated content |
| LCP request discovery | Prioritise LCP image, LCP lazy-loaded |
| LCP breakdown (phases) | Largest Contentful Paint element |
| Network dependency tree | Critical request chains, preconnect |
| Render-blocking requests | Eliminate render-blocking resources |
| Use efficient cache lifetimes | Long cache TTL |
| Layout shift culprits | Layout shifts |
Eight audits were removed with no replacement because, according to Google, they "no longer served useful purposes". They are first-meaningful-paint, font-size, no-document-write, offscreen-images ("Defer offscreen images"), preload-fonts, third-party-facades, uses-passive-event-listeners and uses-rel-preload. Google said there were no signals that font size remains an SEO concern. Lighthouse 13 also requires Node 22.19 or later for anyone running it from the command line.
2026 releases: Baseline and Agentic Browsing
According to the Lighthouse GitHub release notes, the 13.x line has continued to add features:
- 13.1.0 added a Baseline compatibility audit to the default configuration.
- 13.2.0 and 13.3.0 introduced and then enabled an Agentic Browsing category. It checks the accessibility tree, layout stability (CLS), WebMCP tool registration and whether an
llms.txtrequest returns a server error. - 13.5.0 is the latest release on GitHub at the time of writing. It added an Agent Resource Discovery audit and grouped
llms.txtchecks under "agent discovery".
On 22 June 2026, the Chrome team said the Agentic Browsing category is available from Chrome 150. Google's documentation says the category "does not have a weighted average score from 0 to 100". It shows a ratio of checks passed, and Google says it is "experimental and based on proposed standards". The llms.txt audit only checks whether requesting the file causes a server error. A missing file is marked not applicable, and Google says providing one "is optional at the moment".
PageSpeed Insights runs Lighthouse on Google's servers, and the version can lag behind the latest GitHub release. The Lighthouse version is shown at the foot of each report.
What this means for UK businesses
Your score did not drop because of Lighthouse 13. If a site's performance score moved around October 2025, look at real causes such as new scripts, larger images or slower hosting, not the audit renames.
Old checklists and reports may now be out of date. UK agencies with templates built on audit names like "Defer offscreen images" or "Eliminate render-blocking resources" should map them to the new insights. Crawlers that pull PageSpeed data, such as Screaming Frog from version 23.0, have made the same change, and Screaming Frog warned of breaking changes to scheduled reports.
Agentic Browsing is not a ranking factor and not something to chase. Google's own Search guidance says: "You don't need to create new machine readable files, AI text files, markup, or Markdown to appear in Google Search." A clean accessibility tree and low CLS are worth having anyway, for users and for Core Web Vitals.
Field data still matters most for Search. Lighthouse is a lab test. Core Web Vitals in Search Console and the field data section of PageSpeed Insights reflect real Chrome users.
What to do now
- Check which Lighthouse version produced each report before comparing audits across dates.
- Update your audit templates using the table above. Treat "Improve image delivery" and "Document request latency" as the new home of the old image, compression and server-response findings. Our guides on image optimisation and reducing TTFB still apply.
- Re-baseline client reports. Note the change in your next report so clients do not read renamed items as new problems.
- Prioritise Core Web Vitals (LCP, INP and CLS) over individual audit counts. See Core Web Vitals explained.
- Do not rush to add llms.txt for Google. Google's guide to optimising for generative AI features says "Google Search itself doesn't use them". If you do add one for other services, make sure the URL does not return a server error.
- Run a combined check. MakeItFlow runs Lighthouse performance and Core Web Vitals as part of one scan alongside on-page SEO, DNS, email and security checks. You can run a free website audit, and paid plans add scheduled re-scans and history so you can track scores over time.
If you track performance over time, MakeItFlow monitoring re-scans your site daily or weekly and keeps the score history, which makes it easier to tell a jump caused by a Lighthouse version change from a genuine slowdown on your site.
Frequently asked questions
Did Lighthouse 13 change how the PageSpeed performance score is calculated?
No. Google stated that there are no changes to performance scoring in Lighthouse 13. It replaced and removed only non-scored audits. Read more in our guide to PageSpeed Insights scores.
Where did "Defer offscreen images" go?
It was removed in Lighthouse 13 with no direct replacement. Lazy-loading below-the-fold images is still good practice, but do not lazy-load your LCP image. The "LCP request discovery" insight flags that.
Does the Agentic Browsing category affect Google rankings?
Google has not linked it to Search ranking. The Chrome documentation describes it as experimental and unbenchmarked, and Google Search's guidance says no special AI files or markup are needed for AI features.
Sources
- Lighthouse 13 release (Chrome for Developers, 10 October 2025)
- Lighthouse releases (GitHub)
- A developer toolkit to make your website agent-ready (Chrome for Developers, 22 June 2026)
- Lighthouse agentic browsing scoring (Chrome for Developers)
- Guide to Optimizing for Generative AI Features on Google Search (Google Search Central)
- Screaming Frog SEO Spider Update – Version 23.0
Written by the MakeItFlow team
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