devtools-debugging

DevTools debugging

Debug frontend issues by observing the running page, not by guessing from source. The Chrome DevTools MCP drives a real Chrome, so the actual console output, the actual response body, the actual computed style are available directly — which is almost always faster and more correct than reading a component and forming a theory. This skill wires that MCP up, then teaches a reproduce-first loop and four concrete workflows on top of it.

Web only. The DevTools MCP drives Chrome, so this skill is for web. For React Native, debug with the RN DevTools / Flipper instead — out of scope here.

Version targets: chrome-devtools-mcp@latest, current stable Chrome, Node ≥22. Tool names and config grounded against Context7 (/chromedevtools/chrome-devtools-mcp) at authoring time — see references/snippets.md.

First time? Wire up the MCP

If claude mcp list doesn't show chrome-devtools, set it up before debugging — references/setup.md has the runbook. The house default is project scope (committed to the working repo so every frontend dev gets it) running --isolated and headed. You only do this once per repo.

The core loop

Debugging against a live page is a loop, not a guess: reproduce in the running page → observe the real signal (console / network / DOM / screenshot) → form one hypothesis → change one thing → verify in the same page. The discipline here — reproduce before theorizing, change one variable at a time — is owned by superpowers:systematic-debugging; this skill defers to it and adds only what's unique to driving a live Chrome through the MCP.

The rule that makes it pay off: trust the page over the source. When the code says one thing and the running page says another, the page is right. The whole point of the MCP is to stop guessing — so read the signal before you edit.

Principles

• Reproduce first, in the real page. navigate_page to where the bug lives and drive the exact interaction (click, fill_form) that triggers it before you theorize. A bug you can't reproduce in the page, you can't confirm you've fixed.
• Read the signal, don't infer it. The console (list_console_messages), the network (list_network_requests / get_network_request), the DOM (take_snapshot), and the rendered pixels (take_screenshot) are observable — look at them instead of reasoning about what the code "should" do.
• Change one thing, then re-verify in the same page. After an edit, reproduce the same way and confirm the signal changed. An unverified fix is a hypothesis.
• Snapshot for structure, screenshot for appearance. take_snapshot returns the accessible DOM text + element UIDs you act on; take_screenshot shows what the user actually sees. Layout and visual bugs need the screenshot — the DOM can be correct while the pixels are wrong.
• Diagnose performance here, fix it there. A performance_start_trace tells you where the time goes; the fix method (Core Web Vitals, bundle, render cost) lives in frontend-performance. Don't re-derive it.

Workflows

Concrete MCP tool sequences for each, in references/snippets.md:

1. Console error / uncaught exception — navigate, reproduce, list_console_messages, trace to source.
2. Failed or wrong network request — list_network_requests, then get_network_request for the offender; read status/headers/body to split client bug from server bug.
3. DOM / layout / styling bug — take_snapshot for live structure + computed style, take_screenshot to confirm what actually rendered.
4. Performance regression — performance_start_trace (reload), read the bottleneck, then hand off to frontend-performance for the fix.

Deep React-internals / profiler debugging isn't a workflow here — the DevTools MCP doesn't expose React DevTools cleanly. Use the browser React DevTools extension directly for that.

How to use this skill

1. Not wired up yet? Run references/setup.md once for the repo.
2. Run references/checklist.md against the bug — it's ordered reproduce-first.
3. Reach for the matching sequence in references/snippets.md.
4. Check references/pitfalls.md — the live-page traps that waste the most time.

Related

• The debugging discipline (reproduce, isolate, one change at a time) → superpowers:systematic-debugging
• Fixing a performance bottleneck once a trace has found it → frontend-performance
• Capturing the reproduced bug as a regression test after the fix → frontend-testing