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Agent skill

CSS File Size

by thedaviddias in thedaviddias/Front-End-Checklist

A skill your agent uses when auditing slow page loads, heavy assets, or rendering delays related to Optimize CSS file size.

MITAuto-check passedFrontend & Design

Install CSS File Size

skills CLI
$ npx skills add thedaviddias/Front-End-Checklist --skill css-file-size -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install thedaviddias/Front-End-Checklist css-file-size --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/thedaviddias/Front-End-Checklist.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/css-file-size .claude/skills/css-file-size && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
css-file-size
GitHub stars
74k
Token cost
~399 tokens
SKILL.md length
156 words
Files
2 (incl. references)
Skills in repo
390
Repo updated
First seen
Licence
MIT

At a glance

A skill your agent uses when auditing slow page loads, heavy assets, or rendering delays related to Optimize CSS file size.

  • Auditing slow page loads
  • SKILL.md covers Quick Reference, Check, Fix and Explain, plus 1 more section
  • Instructions only: no scripts, shell commands, URLs or credentials in SKILL.md
  • Rendering delays related to Optimize CSS file size

What it does

CSS File Size is an agent skill from thedaviddias/Front-End-Checklist. Use when auditing slow page loads, heavy assets, or rendering delays related to Optimize CSS file size. Verify the actual bottleneck in DevTools, Lighthouse, or field data before recommending changes.

Its SKILL.md is about 400 tokens, which your agent loads only when the skill is triggered. The skill folder holds 2 other files, including reference files (for example `references/rule.md`).

It sits in Frontend & Design, covering Web performance and CSS and styling. The repository describes itself as: 🗂 The essential checklist for modern web development, for humans and AI agents. The licence is MIT.

When your agent uses it

  • Auditing slow page loads
  • Rendering delays related to Optimize CSS file size

Example prompts

  • “/css-file-size”

What it can do on your machine

Read from SKILL.md and the folder at commit e8d14d0. It shows what the files ask for, not the result of running them.

  • Tool permissions

    Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

    From allowed-tools in the SKILL.md frontmatter.

  • Runs code

    No scripts in the folder and no shell commands in SKILL.md.

    From the folder's file list and the shell code blocks in SKILL.md.

  • Network

    Links to these hosts (documentation or services it may open):

    • frontendchecklist.io

    From URLs in SKILL.md, links to its own repository left out.

  • Credentials

    Names no API keys, tokens, secrets or passwords.

    From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

CSS File Size loads about 399 tokens when it runs, and up to ~1.3k if it reads all its reference files. Until then it costs about 54 tokens; SKILL.md has 156 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~54
When it runs · the whole SKILL.md, loaded when a task matches
~399
With references · SKILL.md plus every file in references/, read only if the agent opens them
~1.3k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Auto-check passed

The automated check found no risky patterns in SKILL.md.

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from thedaviddias/Front-End-Checklist at commit e8d14d0, republished under its MIT licence (© thedaviddias). 156 words, ~399 tokens.

Download SKILL.mdSave it as .claude/skills/css-file-size/SKILL.md (or your agent's skills folder). This skill also uses 1 other file; get the full folder from GitHub.
name
css-file-size
description
Use when auditing slow page loads, heavy assets, or rendering delays related to Optimize CSS file size. Verify the actual bottleneck in DevTools, Lighthouse, or field data before recommending changes.
metadata.category
performance
metadata.priority
medium
metadata.difficulty
intermediate
metadata.estimatedTime
10
metadata.source
frontendchecklist.io
metadata.url
https://frontendchecklist.io/rules/performance/css-file-size

Optimize CSS file size

Large CSS files block rendering and increase the time it takes for the browser to construct the CSSOM, leading to a slower First Contentful Paint.

Quick Reference

  • Keep individual CSS files small to speed up parsing and rendering
  • Use minification and remove unused CSS (PurgeCSS)
  • Leverage modular CSS or Tailwind to reduce duplication

Check

Audit the size of CSS files and identify those exceeding recommended limits (e.g., > 50KB gzipped).

Fix

Minify CSS, remove unused styles, and consider splitting large stylesheets into smaller, page-specific files.

Explain

Explain how CSS file size affects the critical rendering path and browser performance.

Code Review

Review the routes, assets, and loading behavior that affect Optimize CSS file size. Flag exact files, requests, or rendering steps that add unnecessary network, CPU, or layout cost, and describe the measurement method used to confirm the issue.

For full implementation details, code examples, and framework-specific guidance, see references/rule.md.

Rule page: https://frontendchecklist.io/rules/performance/css-file-size

© thedaviddias, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 1 other file (references) in skills/css-file-size of thedaviddias/Front-End-Checklist.

  • SKILL.md
  • references/rule.md

Open the folder on GitHubat commit e8d14d0

Compare with similar skills

CSS File Size next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

CSS File Size compared with similar skills
SkillStarsUsed inTokensAuto-checkLicenceRepo updated
CSS File Size this skillthedaviddias/Front-End-Checklist74k—~399Automated safety check: PassMIT
Frontend Guidelightly-ai/lightly-studio896—~2.9kAutomated safety check: PassApache-2.0
Fixing Motion Performanceibelick/ui-skills9.5k5 repos~1.4kAutomated safety check: PassMIT
LobeHub React Component Guidelobehub/lobehub83k—~1.7kAutomated safety check: PassCustom licence
Tailwindcss Developmentanonaddy/anonaddy4.9k10 repos~865Automated safety check: PassMIT
UI StylingOhh-889/skyroc79513 repos~2.5kAutomated safety check: PassMIT

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Categories

Questions about CSS File Size

What does CSS File Size do?

A skill your agent uses when auditing slow page loads, heavy assets, or rendering delays related to Optimize CSS file size. CSS File Size is an agent skill from thedaviddias/Front-End-Checklist. Use when auditing slow page loads, heavy assets, or rendering delays related to Optimize CSS file size.

When should I use CSS File Size?

CSS File Size fits situations like: auditing slow page loads; rendering delays related to Optimize CSS file size.

How do I install CSS File Size in Claude Code?

Run `npx skills add thedaviddias/Front-End-Checklist --skill css-file-size -a claude-code`. Or copy the skill folder (skills/css-file-size in thedaviddias/Front-End-Checklist) into .claude/skills/css-file-size in your project. Claude Code loads it when a task matches its description.

How do I install CSS File Size in Codex?

Run `npx skills add thedaviddias/Front-End-Checklist --skill css-file-size -a codex`. Or copy the skill folder (skills/css-file-size in thedaviddias/Front-End-Checklist) into .agents/skills/css-file-size in your project. Codex loads it when a task matches its description.

Can I use CSS File Size in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add thedaviddias/Front-End-Checklist --skill css-file-size -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/css-file-size, .gemini/skills/css-file-size, .github/skills/css-file-size and .opencode/skills/css-file-size in your project.

What does CSS File Size need to run?

SKILL.md names no scripts, command-line tools or credentials: CSS File Size is instructions for the agent only.

Does CSS File Size access the network?

SKILL.md names 1 domain. As links in the text: frontendchecklist.io. This is read from the text; nothing was executed.

Is CSS File Size safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.

What licence does CSS File Size use?

CSS File Size is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does CSS File Size use?

About 399 tokens (SKILL.md is roughly 1.6k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 900 tokens, read only when the agent opens those files.

What are the alternatives to CSS File Size?

Skills that share tags, products or a category with CSS File Size: Frontend Guide (lightly-ai/lightly-studio, 896 stars), Fixing Motion Performance (ibelick/ui-skills, 9.5k stars), LobeHub React Component Guide (lobehub/lobehub, 83k stars) and Tailwindcss Development (anonaddy/anonaddy, 4.9k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains CSS File Size?

thedaviddias (a GitHub user) maintains it in thedaviddias/Front-End-Checklist, which has 74,412 GitHub stars. The repository holds 390 skills in this directory. The repository was last updated on October 6, 2026.

Source: thedaviddias/Front-End-Checklist on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.