WebPerf Snippets is a collection of JavaScript snippets that run in browser developer tools to measure and debug website performance. It helps developers investigate Core Web Vitals, loading, interaction responsiveness, images, video, scripts, and other performance issues. Its catalogue skills, setting, and instruction support agent-assisted use of the snippets.
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 nucliweb/webperf-snippets --skill webperfgit clone --depth 1 https://github.com/nucliweb/webperf-snippetsWrote 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/nucliweb/webperf-snippets/webperf)<a href="https://agentmods.dev/skills/nucliweb/webperf-snippets/webperf"><img src="https://agentmods.dev/badge/skills/nucliweb/webperf-snippets/webperf/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/nucliweb/webperf-snippets/webperf"><img src="https://agentmods.dev/badge/skills/nucliweb/webperf-snippets/webperf.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00057 | $0.00535 |
| Opus 5.5 | $0.00023 | $0.00214 |
| Sonnet 5.5 | $0.00011 | $0.00107 |
| Haiku 4.5 | $0.00006 | $0.00053 |
Grade A, and why
webperf 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.
What it actually says
WebPerf Snippets Toolkit
A collection of 56 JavaScript snippets for measuring and debugging web performance in Chrome DevTools. Each snippet runs in the page and returns a structured result object.
Quick Reference
| Skill | Snippets | Trigger phrases |
|---|---|---|
| webperf-core-web-vitals | 7 | "debug LCP", "slow LCP", "CLS", "layout shifts", "INP", "interaction latency", "responsiveness" |
| webperf-loading | 34 | "TTFB", "slow server", "FCP", "render blocking", "font loading", "script loading", "resource hints", "service worker" |
| webperf-interaction | 10 | "jank", "scroll performance", "long tasks", "animation frames", "INP debug" |
| webperf-media | 4 | "image audit", "lazy loading", "image optimization", "video audit" |
| webperf-resources | 1 | "network quality", "bandwidth", "connection type", "save-data" |
Workflow
- Identify the relevant skill based on the user's question (see Quick Reference above)
- Load the skill's SKILL.md to see available snippets and thresholds
- Execute with Chrome DevTools MCP:
mcp__chrome-devtools__navigate_page→ navigate to target URLmcp__chrome-devtools__evaluate_script→ run the snippet and read the returned object, which is the result (the scripts have no console output)status: "tracking"→ call the function named ingetDataFnwith anothermcp__chrome-devtools__evaluate_scriptcall after the interactions- Without Chrome DevTools MCP, run the snippet with the CLI:
npx webperf-snippets <url> --snippet <Name> --json
- Interpret results using the thresholds defined in the skill
- Provide actionable recommendations based on findings
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 · -1 lines cb18896d7d57
- 5d ago Changed · +1 lines 0a96ff311526
- 6d ago Changed 36d630705b0a
- 21d ago Changed 22ae259c9f70
- 22d ago Changed d485364e69e1
- 1mo ago First seen · 38 lines · 57 tokens per session scan A a4076330e9a2
webperf is a skill published in the GitHub repository nucliweb/webperf-snippets (1,454 stars, last pushed today), licensed MIT. It adds 57 tokens to every session and 535 once invoked, about $0.0002 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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