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benchmarkcommit 043feff · v1.0.0SKILL.md · Performance

Web Performance Benchmark

Measures live page metrics from performance.getEntries() in a browser and compares them with a saved baseline to detect web performance regressions.

May drive your real signed-in browser through Aside to open the target site, and logs telemetry through gstack scripts.

npx skills add garrytan/gstack --skill benchmark
Permissions
  • read-repo
  • write-files
  • shell
  • network
Compatible with
Claude Code, Codex, Cursor, Copilot
GitHub
138.5k
Source
Community · Garry Tan
Status
Scan passed
License
MIT
Category
Performance
Repository
github.com/garrytan/gstack/benchmark

Core rule

Measure, don't guess: use actual performance.getEntries() data, not estimates.

Execution Phases

  1. Phase 01Set up and pick pages

    Create .gstack/benchmark-reports, then use --pages or propose the homepage plus up to 5 nav targets for the user to confirm; --diff limits it to pages the branch affects.

  2. Phase 02Collect metrics

    Run the browser script 5 times per page for TTFB, FCP, LCP, DOM timings, full load, slow resources and JS/CSS sizes, using medians and ranges.

  3. Phase 03Baseline and compare

    In --baseline mode, save baseline.json; otherwise compare against it with regression thresholds, treating deltas within the run spread as no change.

  4. Phase 04Resources and budget

    List the slowest resources with one remedy each, then check FCP, LCP, JS, CSS, transfer and request budgets and assign a grade.

  5. Phase 05Trends and report

    With --trend, show the last 5 runs; save Markdown and JSON reports under .gstack/benchmark-reports.

Permissions (summarised from SKILL.md)

CapabilityNeededDetails
File writesLimitedOnly writes reports and baselines under .gstack/benchmark-reports; does not modify code unless explicitly asked.
Command executionRequiredRuns gstack scripts, git, gh, and aside repl or the bundled headless browser commands to collect data.
Network outboundLimitedOnly visits the target site the user named and its same-origin pages; --diff mode queries the base branch with gh.

SKILL.md frontmatter (YAML)

SKILL.md frontmatter (YAML)commit 043feff · v1.0.0
---
name: benchmark
preamble-tier: 1
version: 1.0.0
description: Web performance regression detection. (gstack)
triggers:
  - web performance benchmark
  - check page speed
  - detect page performance regression
allowed-tools:
  - Bash
  - Read
  - Write
  - Glob
  - AskUserQuestion
---

Related skills

A rule scan cannot catch every risk. Read this skill's SKILL.md and check its permissions before installing.
Markdown version GitHub