Guide · Agent skill
How to use the Non-Blocking CSS Loading agent skill
Updated · written with AI from the project's own documentation and checked against our catalogue data
The Non-Blocking CSS Loading skill (css-non-blocking) is a short checklist that tells an AI agent how to review a site's stylesheets for render-blocking behavior and suggest fixes. It is aimed at front-end developers who want to speed up a slow-loading page. After this guide you will know what the skill does, how to install it, how to trigger it with plain requests, and where it can go wrong.
Non-Blocking CSS Loadingthedaviddias/Front-End-Checklist · MIT Download the skill Quick start
- 1Download the ZIP. Get the css-non-blocking skill ZIP from the page and unzip it.
- 2Place the folder. Move the folder to ~/.claude/skills/ for personal use, or to .claude/skills/ inside a project.
- 3Or upload it in the apps. In the Claude apps, go to Settings → Capabilities → Skills and upload the skill.
- 4Make a request. Ask in plain language about stylesheets, render blocking or slow first paint.
- 5Provide source files. Make sure the agent can read the project's stylesheets and HTML, since it needs them to review.
- 6Test proposed changes. Check the rendered layout across screen sizes and interaction states before shipping.
What does the skill make the agent do?
Render-blocking CSS delays First Contentful Paint: visitors see a blank screen while the browser downloads and parses stylesheets. With this skill, the agent reviews how your site loads its stylesheets and checks whether they delay the first time a page appears on screen.
It can suggest fixes such as preloading styles, inlining critical CSS, or splitting styles by media query. It then checks the rendered layout across breakpoints and interaction states before proposing a fix.
- Preload stylesheets with a link rel="preload" as="style" tag and an onload handler
- Inline critical above-the-fold CSS and defer non-critical styles
- Use media queries to split CSS by viewport or feature
- Frameworks such as Next.js and Vite often handle this automatically, so check before changing anything
How do you install the css-non-blocking skill?
Download the ZIP for the skill from our page and unzip it. For a personal setup, place the folder in ~/.claude/skills/. To limit it to one project, place it in that project's .claude/skills/ folder.
In the Claude apps, you can instead upload the skill under Settings → Capabilities → Skills.
- Personal: ~/.claude/skills/
- Single project: .claude/skills/ inside the project folder
- Claude apps: Settings → Capabilities → Skills
What files does the skill contain?
The skill has two files. SKILL.md holds the short checklist: a quick reference, plus Check, Fix, Explain and Code Review prompts. references/rule.md is a longer reference guide with a code example and the non-blocking solutions in more detail.
The skill requires nothing to be listed, runs no scripts and uses no network access, so it works from the files alone.
- SKILL.md: the checklist the agent follows
- references/rule.md: the longer guide with code examples
How do you trigger the skill with a natural request?
You do not need a special command. Describe the task in plain language and mention stylesheets, render blocking or page load speed. The skill's description covers reviewing stylesheets, component styles and responsive behavior related to loading CSS without blocking render.
Give the agent access to the source files, because it needs them to review the CSS.
- "Review how this site loads its stylesheets and tell me if any of them block the first paint."
- "Our homepage shows a blank screen before styles appear. Check the CSS loading and suggest a fix."
- "Check the layout at mobile, tablet and desktop widths before we change how styles load."
- "Look at the header and hero styles and suggest what to inline as critical CSS."
What does a typical review look like?
Suppose a page loads styles.css and large-library.css as normal stylesheet links in the head. The reference guide flags this pattern as blocking because it delays DOM parsing. The agent can point to these tags and propose preloading them, inlining critical rules, or splitting styles by media query.
Any proposed change should be tested, because preloading or deferring CSS can cause a flash of unstyled content or broken layouts. Ask the agent to check the rendered result at several screen sizes and interaction states.
<link rel="stylesheet" href="styles.css">
<link rel="stylesheet" href="large-library.css">What should you watch out for?
The skill is a checklist, not a guarantee. It does not run scripts or make network calls, but the changes it suggests will affect how your real pages render, so review them before release. The skill itself notes that frameworks like Next.js and Vite often handle this automatically, so the advice may be redundant in those projects.
Do not apply changes to production styles without testing them first.
- Confirm your framework does not already handle CSS loading
- Test for a flash of unstyled content after any change
- Check layouts across breakpoints and interaction states
What people use it for
- Finding stylesheet links in the head that delay the first paint of a page
- Deciding which above-the-fold CSS to inline as critical styles
- Splitting a large stylesheet by media query so mobile visitors load less CSS
- Reviewing responsive and component styles for layout breaks after a loading change
- Preparing a performance review before a release
Frequently asked questions
How do I install the css-non-blocking agent skill?
Download the ZIP from our page and unzip it into ~/.claude/skills/ for personal use, or into a project's .claude/skills/ folder. You can also upload it in the Claude apps under Settings → Capabilities → Skills.
Does the css-non-blocking skill require anything to run?
The skill lists no requirements. It runs no scripts and uses no network access. It does need access to your site's source files to review the CSS.
Is the css-non-blocking skill free to use?
The skill is released under the MIT licence, as listed on this page. Check the licence file in the source repository for the full terms.
Should I use this skill if I use Next.js or Vite?
Probably not without checking first. The skill notes that Next.js and Vite often handle non-blocking CSS automatically, so its advice may be redundant in those projects.
Why did my page flash unstyled after applying the fix?
Preloading or deferring CSS can cause a flash of unstyled content or broken layouts. Test the page at several screen sizes and interaction states, and keep critical styles inlined so above-the-fold content is styled from the start.
How does this compare to other ways of speeding up CSS?
This skill focuses on the loading order and blocking behaviour of stylesheets. It is a short checklist plus a reference guide, not a full performance audit tool, so pair it with your own testing.
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Our verdict
Use this skill if you are a front-end developer with access to your site's source and want a structured checklist for render-blocking CSS. Skip it if your project already uses a framework that handles CSS loading, or if you cannot test changes before they reach production.
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