Guide · Agent skill
How to use the CSS Minification Checker agent skill
Updated · written with AI from the project's own documentation and checked against our catalogue data
The css-minification skill is a guide for an AI coding agent that reviews your stylesheets, component styles, and responsive behavior to check whether your CSS is minified before release. This page explains what a skill is, how to install this one, how to ask for it in plain language, and what it needs. By the end you will know how to get the agent to review your build setup and explain the changes it suggests.
CSS Minification Checkerthedaviddias/Front-End-Checklist · MIT Download the skill Quick start
- 1Download the ZIP. Download the css-minification skill ZIP from this page.
- 2Unzip into a skills folder. Unzip it into ~/.claude/skills/ for all projects, or into .claude/skills/ inside one project.
- 3Or upload in the Claude apps. In the Claude apps, open Settings → Capabilities → Skills and upload the ZIP instead.
- 4Check your project has a build step. Confirm you use a build tool such as Vite, webpack, or PostCSS, since setup advice depends on it.
- 5Ask in plain language. Request a review, for example checking whether production CSS is minified before release.
- 6Review the suggestions. Read the explanation and suggested tool setup, then test any change in a branch before deploying.
What is an agent skill and what does this one do?
An agent skill is a folder of instructions that an AI agent loads when a task matches the skill's description. This one is based on the rule 'Minify all CSS files' from the Front-End Checklist.
Once installed, the agent focuses on whether CSS is minified before release. It explains that minification shrinks files by removing whitespace, comments, and verbose syntax, and it can suggest build-tool setups such as cssnano, Lightning CSS, or CleanCSS. It can also check rendered layouts across breakpoints and interaction states before proposing a fix.
- Reviews stylesheets, component styles, and responsive behavior
- Explains why minified CSS is smaller
- Suggests build-tool setups (cssnano, Lightning CSS, CleanCSS)
- Flags exact selectors, declarations, or breakpoints that break the rule in the rendered UI
How do you install the css-minification skill?
You can install the skill in one of two ways. Download the ZIP file from the skill's page on this site and unzip it into your personal skills folder, ~/.claude/skills/, or into a project's .claude/skills/ folder if you want it available only for that project.
If you use the Claude apps, you can instead upload the ZIP under Settings → Capabilities → Skills.
- Option 1: download the ZIP from this page and unzip it into ~/.claude/skills/ (all projects)
- Option 2: unzip it into .claude/skills/ inside one project (that project only)
- Option 3: in the Claude apps, go to Settings → Capabilities → Skills and upload the ZIP
What files come with the skill?
The skill contains two files. SKILL.md holds the main instructions and metadata, including the description the agent uses to decide when to load the skill. references/rule.md holds the longer rule page with code examples for unminified and minified CSS and for framework-specific guidance.
You do not need to edit either file to use the skill.
- SKILL.md: main instructions and trigger description
- references/rule.md: full rule details and code examples
How do you trigger the skill with natural requests?
You do not need a special command. Describe what you want in ordinary language that matches the skill's purpose: reviewing stylesheets, checking whether CSS is minified, or preparing a build for production. The agent should load the skill when your request fits its description.
Be specific about your project. Mention your build tool (Vite, webpack, or PostCSS) and the files or components you want reviewed. The more context you give, the more useful the review will be.
- 'Check whether our production CSS is minified before we release.'
- 'Review the styles in src/components/Navigation.css for minification and responsive issues.'
- 'We use Vite. How should I set up CSS minification in the build?'
- 'Compare cssnano and CleanCSS for our PostCSS pipeline.'
What does the skill need before it can help?
The skill's advice assumes your project has a build step. It is designed for projects with a build tool such as Vite, webpack, or PostCSS, because setup changes happen there. If you serve hand-written CSS directly with no bundler, the advice will not fit your setup as written.
You only need cssnano, Lightning CSS, or CleanCSS if you choose one of them. The skill does not run scripts and does not use the network, according to its listing.
- A project with a build tool such as Vite, webpack, or PostCSS (for setup changes)
- Optional: cssnano, Lightning CSS, or CleanCSS, if you choose one of them
- Runs scripts: no
- Uses network: no
What are the safety notes and limits?
The skill provides guidance and review. It does not measure real page speed, and it produces no benchmarks. The rule page mentions a typical 20-40% file size saving from minification, but that is a general claim, not a measurement of your files. Check your own output size with your build tool before you rely on any figure.
Because the skill runs no scripts and makes no network calls, the main risk is acting on advice without testing it. Review every suggested config change in a branch before deploying.
- No measurement of real page speed; use your own tooling to measure
- The 20-40% figure is a general claim, not your result
- Test suggested build changes before production
Tips for getting useful results
Ask the agent to check the rendered layout as well as the CSS. The skill is written to look at breakpoints and interaction states, such as hover, before proposing a fix. Give it the breakpoints you care about and it will flag the exact selectors or declarations that conflict with the rule.
Combining minification with Gzip or Brotli compression is listed as a way to get more savings, so ask the agent how your server handles compression.
- Name the breakpoints and interaction states you care about
- Share the build config file so suggestions match your setup
- Ask for the reason behind each suggested change
What people use it for
- Auditing whether production CSS is minified before a release
- Setting up CSS minification in a Vite, webpack, or PostCSS build
- Comparing cssnano, Lightning CSS, and CleanCSS for a project
- Reviewing component styles and responsive breakpoints before proposing a fix
- Learning why minification reduces file size, as a guided beginner explanation
Frequently asked questions
How do I install the css-minification skill?
Download the ZIP from this page and unzip it into ~/.claude/skills/ for all projects, or into .claude/skills/ inside a single project. In the Claude apps, you can instead upload the ZIP under Settings → Capabilities → Skills.
Is the css-minification skill free to use?
The skill is published under the MIT licence, as listed on this page. Check the licence file in the source repository for the full terms.
What does the css-minification skill require?
It requires a project with a build tool such as Vite, webpack, or PostCSS for setup changes. cssnano, Lightning CSS, or CleanCSS are optional, used only if you choose them. It runs no scripts and uses no network.
Does the skill measure how fast my site loads?
No. The skill provides guidance and review, not benchmarks or real speed measurements. The 20-40% savings figure on the rule page is a general claim, so measure your own files with your build tool.
Can I use this skill if I don't use a build tool?
The advice assumes a bundler is available, so it fits projects with a build step less well. If you serve hand-written CSS directly with no bundler, the setup suggestions will not match your project as written.
How is this different from just running a minifier?
A minifier only compresses files. This skill reviews your stylesheets, component styles, and responsive behavior, explains why minification helps, and suggests which build-tool setup to use. It is guidance for an agent, not a tool that changes your files on its own.
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Our verdict
Use this skill if you are a front-end developer setting up or auditing a build pipeline, a team checking performance before release, or a beginner who wants a guided explanation of CSS minification. Pick something else if your project serves hand-written CSS with no build step, or if you need real page speed measurements rather than review and guidance.
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