modern-web-guidance-src: Replace outdated patterns used by coding agents with 250 modern web APIs

LLM-based coding agents tend to replicate outdated code patterns found in their training data. This leads to the generation of unnecessary JavaScript to replace native features already supported by browsers, or the introduction of heavy polyfills. Modern Web Guidance directly injects up-to-date web platform knowledge into these agents' context to block the use of outdated patterns.

This project, jointly maintained by the Google Chrome, Microsoft Edge, Mozilla Firefox, and MDN teams, provides guidelines covering over 250 modern web features. It spans various areas including CSS layout, performance optimization, accessibility, native form components, and browser-embedded AI APIs, focusing on practical, up-to-date implementation patterns while excluding basic content that models already know.

It is a skill set designed for direct consumption by agents, not just documentation. You can use the CLI to search for guides on specific topics or scan existing codebases for outdated patterns that need modernization. It helps generate production-ready code by encouraging the use of platform-level APIs that browsers can optimize and providing lightweight fallback strategies.

It is suitable for developers who use AI coding tools but want to ensure the quality and modernity of the generated code. It is particularly useful for improving agent output quality in projects that must apply the latest web standards such as View Transitions, Popover API, and Container Queries.