Chrome DevTools MCP is an MCP server that lets coding agents control and inspect a live Chrome browser for automation, debugging, screenshots, network analysis, console inspection, and performance tracing. It is for developers who want AI coding assistants to test and diagnose web applications, and the catalogue add-ons provide workflows for using those browser tools.
Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add ChromeDevTools/chrome-devtools-mcp --skill debug-optimize-lcpgit clone --depth 1 https://github.com/ChromeDevTools/chrome-devtools-mcpWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/chromedevtools/chrome-devtools-mcp/debug-optimize-lcp)<a href="https://agentmods.dev/skills/chromedevtools/chrome-devtools-mcp/debug-optimize-lcp"><img src="https://agentmods.dev/badge/skills/chromedevtools/chrome-devtools-mcp/debug-optimize-lcp/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/chromedevtools/chrome-devtools-mcp/debug-optimize-lcp"><img src="https://agentmods.dev/badge/skills/chromedevtools/chrome-devtools-mcp/debug-optimize-lcp.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- Socket pass
- Snyk warn
- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to medium
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- medium Excessive Agency · line 29 Skill enables autonomous high-impact decisions without human-in-the-loop verification. Critical operations (destructive commands, financial transactions, data deletion) should require explicit user confirmation.Fix: Add human-in-the-loop confirmation for destructive, irreversible, or high-impact operations. Never auto-execute commands that modify files, send data, or alter system state.
What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00099 | $0.01569 |
| Opus 5.5 | $0.00040 | $0.00628 |
| Sonnet 5.5 | $0.00020 | $0.00314 |
| Haiku 4.5 | $0.00010 | $0.00157 |
Grade A, and why
debug-optimize-lcp scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
Copies of this mod
8 near-identical copies found in the catalogue:
- debug-optimize-lcp — 100% identical, 2 lines differ
- debug-optimize-lcp — 98% identical, 2 lines differ
- debug-optimize-lcp — 92% identical, 18 lines differ
- debug-optimize-lcp — 92% identical, 18 lines differ
- debug-optimize-lcp — 92% identical, 18 lines differ
- debug-optimize-lcp — 92% identical, 2 lines differ
- debug-optimize-lcp — 92% identical, 18 lines differ
- debug-optimize-lcp — 92% identical, 18 lines differ
How it starts
The opening of the file, as written. The whole thing — 122 lines — stays where its author put it; the contents beside it link to each section on GitHub.
What is LCP and why it matters
Largest Contentful Paint (LCP) measures how quickly a page's main content becomes visible. It's the time from navigation start until the largest image or text block renders in the viewport.
- Good: 2.5 seconds or less
- Needs improvement: 2.5–4.0 seconds
- Poor: greater than 4.0 seconds
LCP is a Core Web Vital that directly affects user experience and search ranking. On 73% of mobile pages, the LCP element is an image.
LCP Subparts Breakdown
Every page's LCP breaks down into four sequential subparts with no gaps or overlaps. Understanding which subpart is the bottleneck is the key to effective optimization.
| Subpart | Ideal % of LCP | What it measures |
|---|---|---|
| Time to First Byte (TTFB) | ~40% | Navigation start → first byte of HTML received |
| Resource load delay | <10% | TTFB → browser starts loading the LCP resource |
| Resource load duration | ~40% | Time to download the LCP resource |
| Element render delay | <10% | LCP resource downloaded → LCP element rendered |
The "delay" subparts should be as close to zero as possible. If either delay subpart is large relative to the total LCP, that's the first place to optimize.
Common Pitfall: Optimizing one subpart (like compressing an image to reduce load duration) without checking others. If render delay is the real bottleneck, a smaller image won't help — the saved time just shifts to render delay.
Debugging Workflow
Follow these steps in order. Each step builds on the previous one.
Step 1: Record a Performance Trace
Navigate to the page, then record a trace with reload to capture the full page load including LCP:
navigate_pagewithpageIdto the target URL.performance_start_tracewithpageId,reload: trueandautoStop: true.
What ships with it
4 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 2d ago Changed d6486b728d7c
- 1mo ago First seen · 122 lines · 99 tokens per session scan A 8898b35108b1
debug-optimize-lcp is a skill published in the GitHub repository ChromeDevTools/chrome-devtools-mcp (53,607 stars, last pushed today), licensed Apache-2.0. It adds 99 tokens to every session and 1,569 once invoked, about $0.0004 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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