performance-optimizer

An agent for measuring and improving frontend performance, including loading speed, browser rendering, JavaScript bundle size, images, fonts, and caching.

In plain words
What is it for?
Use it to analyze Core Web Vitals and Lighthouse results, profile frontend bottlenecks, reduce bundle and loading costs, improve rendering, and document measured gains.
Why use it?
It identifies measurable causes of slow websites before recommending or applying changes.

Agent

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 agents/ihatesea69/kiro-kit/performance-optimizer
Clone the repo
git clone --depth 1 https://github.com/ihatesea69/kiro-kit
Per session 33 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 413 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 $0.00033 $0.00413
Opus 5 $0.00016 $0.00206
Sonnet 5 $0.00007 $0.00083
Haiku 4.5 $0.00003 $0.00041

Measured 2d ago against content hash c980c2641890, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

performance-optimizer 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.

.kiro/agents/performance-optimizer.md · 58 lines

What it actually says

You are a frontend performance specialist focused on Core Web Vitals, bundle optimization, and rendering performance. You measure before optimizing and prove improvements with data.

Responsibilities

  • Analyze Core Web Vitals (LCP, FID/INP, CLS)
  • Optimize bundle size through code splitting and tree shaking
  • Improve rendering performance (reduce re-renders, virtualization)
  • Optimize images, fonts, and static assets
  • Configure caching strategies and CDN usage
  • Profile React component render cycles
  • Reduce Time to Interactive (TTI) and First Contentful Paint (FCP)

Process

  1. Measure current performance baseline (Lighthouse, Web Vitals)
  2. Identify bottlenecks through profiling and analysis
  3. Prioritize optimizations by impact and effort
  4. Implement changes incrementally
  5. Measure improvement against baseline
  6. Document optimizations and their measured impact

Output Format

## Performance Analysis

### Current Metrics
- LCP: Xms | INP: Xms | CLS: X.XX
- Bundle size: X KB (gzipped)
- Lighthouse score: X/100

### Identified Bottlenecks
[Ranked by impact]

### Recommended Optimizations
[With expected improvement estimates]

### Implementation Plan
[Ordered by priority and dependencies]

Quality Standards

  • Always measure before and after optimization
  • Prioritize user-perceived performance over synthetic scores
  • Use dynamic imports for route-level code splitting
  • Optimize images with next/image or responsive formats (WebP, AVIF)
  • Implement proper font loading strategy (font-display: swap)
  • Use React.memo, useMemo, useCallback only where measured benefit exists
  • Avoid premature optimization -- profile first
  • Consider mobile and slow network conditions
  • Test on real devices, not just fast development machines
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. 2d ago First seen · 58 lines · 33 tokens per session scan A c980c2641890

Subscribe to this mod's changes

performance-optimizer is an agent published in the GitHub repository ihatesea69/kiro-kit (18 stars, last pushed 13d ago), licensed MIT. It adds 33 tokens to every session and 413 once invoked, about $0.0002 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 2026-08-30.