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LGJ-Jonathan
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benchmark

Detects web performance regressions by comparing page metrics against captured baselines.

Updated Mar 26, 2026
Search Tags:#performance#web vitals#bundle size#benchmark#baseline#regression detection#page speed
One-click install
npx skills add https://github.com/LGJ-Jonathan/Jonathan_Global_Claude_Skills --skill benchmark-lgj-jonathan
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: benchmark
Source: https://github.com/LGJ-Jonathan/Jonathan_Global_Claude_Skills/tree/main/gstack/benchmark
Command: npx skills add https://github.com/LGJ-Jonathan/Jonathan_Global_Claude_Skills --skill benchmark-lgj-jonathan

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve? Web performance degrades gradually across pull requests, and teams often notice only after load times have doubled. This Skill measures real page performance with the browse daemon, captures baselines, and flags regressions before they ship. ## Core Features & Use Cases - Baseline Capture & Comparison: Record TTFB, FCP, LCP, DOM timings, transfer sizes, and request counts per page, then diff current metrics against the stored baseline with regression thresholds. - Resource & Bundle Analysis: List the slowest resources, track JS/CSS bundle sizes, and check results against industry performance budgets with a letter grade. - Trend Tracking: Use --trend to chart performance across historical benchmark runs, or --diff to benchmark only pages affected by the current branch. - Use Case: Before merging a PR, run /benchmark https://staging.example.com to compare Core Web Vitals against the baseline and catch a 270KB JS bundle increase before it reaches production. ## Quick Start Ask the AI to run /benchmark against your staging URL with the --baseline flag first, then rerun it after your changes to see a regression report.

Frequently Asked Questions about benchmark

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I detect performance regressions before merging a PR?▼

Capture a baseline with /benchmark <url> --baseline on the main branch, then run /benchmark <url> on your feature branch. The skill compares TTFB, FCP, LCP, transfer size, and bundle size, flagging regressions over 50% or 500ms.

How to measure Core Web Vitals from the command line?▼

Use the browse daemon's perf command plus JavaScript evaluation of performance.getEntriesByType to extract FCP, LCP, TTFB, and DOM timings. The skill automates this collection and formats the results into a report.

Can I benchmark only the pages changed in my branch?▼

Yes, run /benchmark --diff to compare the current branch against the base branch using git diff, then benchmark only the affected pages. You can also pass explicit pages with --pages /,/dashboard,/api/health.

What counts as a performance regression in the report?▼

Timing metrics regress when they increase over 50% or by more than 500ms absolute; over 20% is a warning. Bundle sizes regress at over 25% growth, and request counts over 30% trigger a warning.

Does the benchmark skill modify my application code?▼

No, the skill is read-only. It measures pages, writes reports to .gstack/benchmark-reports/, and lists recommendations, but it never edits source code unless you explicitly ask.

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