Modern Web Guidance, a library that tells AI coding agents how to write current web code, left preview with a 1.0 release on Tuesday, November 10. Chrome, Edge, Firefox, and MDN teams now steward it with the web development community. The GitHub release notes, published by Google Chrome, list 203 use-case guides spanning 250 web platform features.
The headline addition for technical teams is legacy-scan, a static scanner that finds outdated web patterns and links each one to a guide with the current replacement. Only about 20% of guides have deterministic legacy rules today, so coverage is partial. Agents follow a four-step workflow: scan, verify, report, modernize.
Performance guidance now addresses splitting long tasks to help Interaction to Next Paint, plus image preloading aimed at LCP. A new public dashboard shows eval results for each agent and each guide.
The notes do not say whether agents following these guides improve field Core Web Vitals. Eval pass rates measure guide adherence, not Search Console outcomes.
Teams letting coding agents edit production templates should run legacy-scan on a staging branch and compare its performance advice with their own field data.
Google Chrome, Modern Web Guidance v1.0.0 release notes on GitHub, November 10, 2026.
