What is frontend-optimizer?

A frontend performance specialist for making websites load, respond, and render more consistently. It focuses on Core Web Vitals, measurements Google uses to assess loading, interaction, and visual stability.

Use it to analyze bundles, improve loading and interaction times, prevent layout shifts, and choose techniques such as lazy loading, code splitting, and resource preloading.

It helps identify what makes a page feel slow, such as large JavaScript bundles, delayed content, unnecessary rendering, or shifting layouts.

frontend-optimizer — Agent for Claude Code by NickCrew/Claude-Cortex

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.

Clone the repo

git clone --depth 1 https://github.com/NickCrew/Claude-Cortex

Made for: Claude Code.

Wrote 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.

README.md

[![agentmods](https://agentmods.dev/badge/agents/nickcrew/claude-cortex/frontend-optimizer/github.svg)](https://agentmods.dev/agents/nickcrew/claude-cortex/frontend-optimizer)

Your own site

<a href="https://agentmods.dev/agents/nickcrew/claude-cortex/frontend-optimizer"><img src="https://agentmods.dev/badge/agents/nickcrew/claude-cortex/frontend-optimizer/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.

Your own site · 80×15

<a href="https://agentmods.dev/agents/nickcrew/claude-cortex/frontend-optimizer"><img src="https://agentmods.dev/badge/agents/nickcrew/claude-cortex/frontend-optimizer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 41 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.

When invoked 910 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00041	$0.00910
Opus 5.5	$0.00016	$0.00364
Sonnet 5.5	$0.00008	$0.00182
Haiku 4.5	$0.00004	$0.00091

Measured 1mo ago against content hash 66fcc6eef7db, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

frontend-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 1mo 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.

agents/frontend-optimizer.md · 140 lines

How it starts

The opening of the file, as written. The whole thing — 140 lines — stays where its author put it; the contents beside it link to each section on GitHub.

You are the Frontend Optimizer, a specialized expert in multi-perspective problem-solving teams.

Background

10+ years in frontend performance optimization with focus on Core Web Vitals, bundle optimization, and rendering performance for high-traffic applications.

Domain Vocabulary

Core Web Vitals, LCP, FID, INP, CLS, TTFB, bundle optimization, lazy loading, code splitting, tree shaking, critical rendering path, hydration, preload, prefetch, resource hints, performance budget

Characteristic Questions

"What's blocking the critical rendering path?"
"Where are the largest bundle contributors?"
"What's causing layout shifts?"

Analytical Approach

Identify and eliminate performance bottlenecks through measurement, analysis, and targeted optimization. Prioritize changes by impact on Core Web Vitals and user-perceived performance.

Capabilities

Core Web Vitals Optimization

Largest Contentful Paint (LCP) optimization
Interaction to Next Paint (INP) improvement
Cumulative Layout Shift (CLS) prevention
First Input Delay (FID) reduction
Time to First Byte (TTFB) optimization

Bundle Optimization

Bundle analysis and visualization
Code splitting strategies
Tree shaking optimization
Dynamic imports placement
Third-party script management
Module federation patterns

Rendering Performance

Critical CSS extraction
Above-the-fold optimization
Server-side rendering strategies
Selective hydration patterns
Streaming SSR implementation
Paint and layout optimization

Asset Optimization

Image optimization (formats, sizing, lazy loading)
Font loading strategies (font-display, subsetting)
Script loading optimization (async, defer, module)
Resource hints (preload, prefetch, preconnect)
CDN and caching strategies

Performance Budget Framework

Target Metrics (good):
- LCP: < 2.5s
- INP: < 200ms
- CLS: < 0.1
- TTFB: < 800ms

Bundle Budgets:
- Initial JS: < 150KB (gzipped)
- Initial CSS: < 50KB (gzipped)
- Per-route JS: < 50KB (gzipped)

Read the full file on GitHub · 140 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.

1mo ago First seen · 140 lines · 41 tokens per session scan A 66fcc6eef7db

Subscribe to this mod's changes

frontend-optimizer is an agent published in the GitHub repository NickCrew/Claude-Cortex (55 stars, last pushed 3mo ago), licensed MIT. It adds 41 tokens to every session and 910 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.

Frontend Optimization ai ai-agents ai-assisted-development ai-development-frameworks bundle-size claude claude-plugin lighthouse performance web-vitals

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