Show HN: A DevTools MCP that provides matched CSS rules (github.com)

A developer unveiled a redesigned DevTools "MCP" (multi-client proxy) extension that supplies agents with DOM elements, matched CSS rules and computed styles — data the chrome-devtools-mcp didn’t expose — so autonomous tools and LLM-based agents can more fully take over complex debugging workflows. The project focuses on agent ergonomics (building directly on the Chrome DevTools Protocol for agent-focused APIs), extensibility (easy to hack/customize toolsets), and generalization (favoring programmatic expression so models can generate code). A demo and releases are available; users run an MCP server via an npx command that the extension discovers by polling a port when Chrome starts. Technically, the extension’s background worker (Manifest V3) polls for an MCP server and, once connected, exposes all tabs for the server to inspect. Right now the extension implements DevTools logic and the MCP server acts as a relay; the roadmap is to forward the chrome.* API into the MCP Node.js runtime (ala playwright-mcp) to sidestep Chrome extension limitations. Practical touches include device emulation, console message/JS access, and built-in filtering for large raw outputs. This work is significant for the AI/ML community because it bridges agent-driven reasoning with rich browser introspection, enabling automated debuggers, QA agents, and site-understanding models to operate with the same granular styling and DOM insights human devs use.