Guide · Agent skill
How to use the JavaScript Code Splitting Review agent skill
Updated · written with AI from the project's own documentation and checked against our catalogue data
The code-splitting skill is a set of review instructions that you give to an AI agent such as Claude. It teaches the agent to look at a JavaScript app and find code that is not needed for the first screen, so that the browser downloads that code later instead of up front. This guide explains what the skill makes the agent do, how to install it, how to ask for a review in plain language, and what to check before trusting its suggestions.
JavaScript Code Splitting Reviewthedaviddias/Front-End-Checklist · MIT Download the skill Quick start
- 1Download the ZIP. Download the code-splitting skill ZIP from this directory page.
- 2Unzip into a skills folder. Extract it into ~/.claude/skills/ for personal use or into your project's .claude/skills/ folder.
- 3Or upload in the Claude apps. Open Settings, go to Capabilities, and upload the skill under Skills.
- 4Ask for a review. Describe a large bundle, new dependency or slow route and name the file or pull request.
- 5Check each suggestion. Read the proposed dynamic import() changes and confirm they keep the first view working.
- 6Measure the result. Use your own bundle visualizer or performance tools to confirm the change helped.
What the code-splitting skill makes the agent do
Code splitting means a web app only downloads the code needed for the current screen. The skill is written for reviewing large single-page app (SPA) bundles, new dependency additions and routes that feel slow to hydrate. When it is active, the agent looks for code that is not required for the initial view and checks whether it could move behind a route transition, a user action or viewport-based loading.
The skill's main recommendations are to use dynamic import() to load code only when it is needed, split routes so each page loads only its own code, lazy-load heavy third-party libraries such as chart libraries or rich text editors, and analyse the bundle with a visualizer to find what to split. The skill is guidance from a checklist. It does not change your files on its own, and it does not run profilers or bundlers.
Install the skill from a ZIP file
Download the ZIP file for the skill from this directory page. Unzip it so that the skill folder, which contains SKILL.md and references/rule.md, ends up in one of two places. For a personal setup that applies to all your projects, use ~/.claude/skills/. For a single project, put it in the project's .claude/skills/ folder.
If you use the Claude apps instead, open Settings, go to Capabilities, and upload the skill under Skills.
- Personal install: ~/.claude/skills/
- Project install: .claude/skills/ inside your project
- Claude apps: Settings → Capabilities → Skills
Trigger the skill with a natural request
You do not need a special command. The skill's description tells the agent when to use it, so you trigger it by asking for a review of the kind it covers. Describe the situation: a large bundle, a new dependency, or a route that feels slow. Name the files or pull request if you have them.
Good requests state the goal and the scope. The agent will then read the code you point it to and report what could be split.
- Review this route module and tell me what could be lazy-loaded with import().
- This PR adds a chart library. Check whether it needs to load on the first screen.
- Our dashboard feels slow to become interactive. Look at the imports in the main route files for code splitting opportunities.
- Convert the static editor import in this component to a dynamic import with a loading state.
Examples of what the agent suggests
The source gives a simple pattern. A static import loads a module with the page. A dynamic import loads it only when a user needs it. In the example below, the PDF generator is loaded when the export button is clicked rather than at startup.
When you ask for a fix, the skill expects the agent to convert the identified static imports to import() calls and add an appropriate loading state. Review each change, since the agent is working from the code you show it.
async function handleExportClick() {
const { generatePDF } = await import('./pdf-generator.js')
generatePDF(document)
}What you need before you start
The skill's metadata lists no required tools, no scripts and no network access. Its SKILL.md says the skill is for intermediate developers. You will get the most out of it if you already have a JavaScript or front-end project to point the agent at, and if you can read the code it suggests changing.
The skill is most useful for a single-page app that feels slow to load, or for pull requests that add large third-party libraries. It is less useful for static sites or server-rendered pages with little client JavaScript, where the gains are small.
- Requires: nothing listed in the skill metadata
- Runs scripts: no
- Uses network: no
Safety notes and limits
According to the skill metadata, it runs no scripts and uses no network. It is review guidance only. The agent reads the code you provide and suggests changes. It cannot measure real load times from this skill alone, so any performance claim should be checked with your own tools.
Treat suggestions as proposals. Check that moving a module does not break the first meaningful paint or any behaviour that depends on load order.
Tips for better results
Give the agent the specific route or file, not the whole repository at once. Ask it to explain its reasoning for each suggested split. Use the bundle visualizer that your build setup provides to confirm which modules are large, then ask the agent to focus on those. Ask for a loading state with every import() change so users are not left with a blank area.
- Point the agent at one route or pull request at a time
- Ask why each module can move, not only what to move
- Confirm large modules with a bundle visualizer before changing code
What people use it for
- Reviewing a pull request that adds a large chart or editor library
- Finding which route modules load code the first screen never uses
- Converting a static import of a PDF or export feature into a dynamic import() triggered by a button
- Explaining how route-based splitting works to a developer learning the technique
Frequently asked questions
How do I install the code-splitting agent skill?
Download the skill ZIP from this page and unzip it into ~/.claude/skills/ for personal use, or into a project's .claude/skills/ folder. In the Claude apps, you can instead upload it under Settings, then Capabilities, then Skills.
What does the code-splitting skill require?
The skill metadata lists no required tools, runs no scripts and uses no network access. You need a JavaScript project to review and an agent that can read the files you share.
Is the code-splitting skill free?
The skill is published under the MIT licence. This page does not list any price, so check the directory page for current terms.
Does the skill run a bundler or profiler?
No. The skill provides review guidance only and does not run profilers or bundlers. You need your own bundle visualizer or performance tools to measure results.
What is the difference between a static import and a dynamic import()?
A static import loads a module together with the page at startup. A dynamic import() loads it only when the code runs, such as when a user clicks a button, so the browser downloads it later.
When should I not use this skill?
Skip it for static sites or server-rendered pages with little client JavaScript, where the gains from splitting are small. It is also not a tool for measuring performance.
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Our verdict
Use this skill if you maintain a single-page app that feels slow to load, or you review pull requests that add large third-party libraries, and you want an agent to suggest where dynamic import() and route splitting could help. Pick something else if you need the agent to run builds or measure performance, or if your site is mostly static or server-rendered with little client JavaScript.
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