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 agentmods add skills/async23/chrome-devtools-mcp/debug-optimize-lcpnpx skills add Async23/chrome-devtools-mcp --skill debug-optimize-lcpgit clone --depth 1 https://github.com/Async23/chrome-devtools-mcpWhat 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 | $0.00099 | $0.01524 |
| Opus 5 | $0.00049 | $0.00762 |
| Sonnet 5 | $0.00020 | $0.00305 |
| Haiku 4.5 | $0.00010 | $0.00152 |
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 yesterday.
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.
This is a copy
92% identical to debug-optimize-lcp — 18 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
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_pageto the target URL.performance_start_tracewithreload: 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.
- yesterday First seen · 122 lines · 99 tokens per session scan A 3617cbbc6437
debug-optimize-lcp is a skill published in the GitHub repository Async23/chrome-devtools-mcp (0 stars, last pushed 16d ago), licensed Apache-2.0. It adds 99 tokens to every session and 1,524 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. It is 92% identical to debug-optimize-lcp, differing in 18 lines, and is treated as a copy.
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