perf

A command for checking the size and performance of a Next.js web application. It examines JavaScript bundles and readiness for Core Web Vitals, which are Google's measures of loading, responsiveness, and visual stability.

In plain words
What is it for?
Use it to inspect bundle output, find heavy client-side imports, check for the bundle analyzer, and review Core Web Vitals readiness.
Why use it?
It helps locate large dependencies and performance bottlenecks before they make a site slower for visitors.

Command

Install

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.

agentmods
npx agentmods add commands/iwritec0de/app-dev/perf
Clone the repo
git clone --depth 1 https://github.com/iwritec0de/app-dev
Per session 10 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 992 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00010 $0.00992
Opus 5 $0.00005 $0.00496
Sonnet 5 $0.00002 $0.00198
Haiku 4.5 $0.00001 $0.00099

Measured yesterday against content hash 8da9df13182b, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

perf 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.

commands/perf.md · 139 lines

How it starts

The opening of the file, as written. The whole thing — 139 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Next.js Performance

Analyze bundle size, identify heavy dependencies, and check Core Web Vitals readiness.

Load the nextjs-expert skill for performance optimization patterns.

Usage

/perf [--bundle] [--vitals]

Arguments

Parse $ARGUMENTS to extract:

  • --bundle — Focus on bundle size analysis
  • --vitals — Focus on Core Web Vitals readiness
  • No flags = run both

Instructions

Bundle Analysis

1. Check for Bundle Analyzer
grep -q "@next/bundle-analyzer" package.json && echo "installed" || echo "not installed"

If not installed, recommend:

npm install -D @next/bundle-analyzer
2. Analyze Build Output

If a .next directory exists from a recent build:

ls -lhS .next/static/chunks/*.js 2>/dev/null | head -20

If no build exists, suggest running npm run build and reading the output.

3. Dependency Impact Analysis

Search for heavy client-side imports:

# Check for heavy libs in client components
grep -r "'use client'" --include="*.tsx" --include="*.ts" -l

For each client component, check imports for known heavy packages:

  • moment (330KB) → suggest dayjs (2KB) or date-fns
  • lodash (72KB) → suggest lodash-es with tree shaking or individual imports
  • @fortawesome/fontawesome (1.5MB) → suggest lucide-react or @heroicons
  • chart.js (200KB) → suggest wrapping in next/dynamic
  • three.js (600KB) → must be dynamically imported
  • @mui/material — Check if tree-shaking properly (named imports)
  • axios (13KB) → native fetch works in Next.js
4. Image Optimization Check
grep -rn "<img " --include="*.tsx" --include="*.jsx" | grep -v "node_modules"
grep -rn "next/image" --include="*.tsx" --include="*.jsx" | head -5

Report:

  • Number of <img> tags (should be zero — use next/image)
  • Missing width/height or fill on Image components
  • Missing sizes prop on responsive images
  • Large images without priority on above-the-fold content

Read the full file on GitHub · 139 lines

Changes

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.

  1. yesterday First seen · 139 lines · 10 tokens per session scan A 8da9df13182b

Subscribe to this mod's changes

perf is a command published in the GitHub repository iwritec0de/app-dev (3 stars, last pushed 4mo ago), licensed MIT. It adds 10 tokens to every session and 992 once invoked, about $0.0001 per session on Opus 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 2026-08-31.