🧭Google, Microsoft, Mozilla and Chrome Teams Ship Modern Web Guidance for Coding Agents

Your coding agent is about to stop writing 2015 code

Browser vendors just gave coding agents a cheat sheet for the modern web. Modern Web Guidance is a set of skills from the Chrome, Edge, Firefox and MDN teams, plus the wider web dev community, that injects platform expertise straight into the agent's context window. If your agent keeps reaching for legacy libraries, this is aimed at you. The guides push models toward platform APIs the browser can optimize, with built-in accessibility, and toward lightweight fallbacks instead of heavy polyfills. Install it through the Quickstart wizard, and the CLI pulls targeted guidelines into the agent on demand. The coverage is broad. There are 250 modern web features, including 140 CSS and layout features like container queries and subgrid. Another 36 cover HTML and DOM, such as declarative shadow DOM, and 74 cover JavaScript and APIs, including the Sanitizer and Scheduler APIs. Then there are 203 real-world use cases, from accessibility to performance work. The guides are token-efficient on purpose. Evals prune anything models already know, so you aren't paying context for stuff the model got right anyway.