Your app worked great in development. You built it with Claude Code or Cursor, shipped it, got users. And now... it feels sluggish. Pages take too long to load. Typing feels laggy. Mobile users are complaining.
You're not imagining it. And you're not alone.
TL;DR
AI-generated React code has three common performance killers: waterfall requests (data loading sequentially instead of in parallel), bundle bloat (downloading unnecessary JavaScript), and re-render madness (the whole app redrawing when you type one character). Vercel just released 45 rules specifically for AI coding tools to catch these issues. Scroll down to see interactive demos of each problem.
Vercel, the company behind Next.js, just released something that validates what many vibe coders have experienced: AI-generated React code often has hidden performance problems. Their response? A set of 45 rules specifically designed for AI coding tools to catch these issues before they ship.
This is significant. When Vercel, one of the most influential companies in React development, creates a ruleset specifically for AI coding assistants, it means the problem is real and widespread enough to address systematically.
Let me break down what this means for you.
What Vercel Actually Released
Vercel published their React Best Practices as an "Agent Skill" - a set of instructions that tools like Claude Code and Cursor can follow when writing or reviewing your code.
The rules are organized by impact level: CRITICAL, HIGH, MEDIUM, and LOW. The critical ones address problems that, in Vercel's words, "create cumulative costs across every user session."
Here's the key insight from their announcement:
Most performance work fails because it starts too low in the stack. If a request waterfall adds 600ms of waiting time, it doesn't matter how optimized your useMemo calls are.
In plain English: the big performance problems aren't about fancy optimizations. They're about fundamental patterns that AI tends to get wrong.
The 3 Performance Killers in Vibe-Coded React
Based on Vercel's CRITICAL and HIGH priority rules, here are the three biggest performance issues I see in AI-generated React code - translated into terms that don't require a computer science degree.
1. Waterfall Requests - When Your App Waits in Line
What you experience: You click something and watch a spinner. Then another spinner. Then another. The page loads in stages, each one waiting for the previous one to finish.
What's actually happening: Your app is fetching data sequentially instead of in parallel. Imagine going to a coffee shop where you have to wait for each person's drink to be made before the barista even takes the next order. That's what sequential data fetching does to your app.
Why AI creates this: AI coding tools tend to write code one piece at a time, following a logical sequence. "First get the user, then get their orders, then get the product details for each order." Logical, yes. Efficient, no. Those requests could all happen at once.
One developer documented this exact problem when testing Claude Code to build a React app. The app worked but had "a lot of slow interactions" that required extensive back-and-forth to fix.
The fix in human terms: Data that doesn't depend on each other should load at the same time. It's like ordering everyone's drinks at once and letting the barista make them in parallel.
2. Bundle Bloat - When Your App Downloads Too Much
What you experience: The app takes forever to load initially, especially on mobile or slower connections. Users see a blank screen for seconds before anything appears.
What's actually happening: Your app is forcing users to download a massive JavaScript file before anything can render. This file contains every library the AI decided to use, even the ones only needed for that one settings page nobody visits.
Why AI creates this: AI tools love libraries. Need to format a date? Here's moment.js (290KB). Need a dropdown? Here's a full component library. Each individual choice seems reasonable, but they compound. Research from Google's Addy Osmani found that AI tools often add libraries inconsistent with the rest of your stack, leading to duplicate functionality and bloated bundles.
The fix in human terms: Not everything needs to load immediately. The code for your admin dashboard shouldn't download when someone just wants to see your homepage. This is called "code splitting" and it's one of Vercel's CRITICAL priorities.
3. Re-render Madness - When Your App Stutters
What you experience: Typing in a form feels laggy. Scrolling stutters. The whole app feels like it's thinking too hard about everything you do.
What's actually happening: Every time anything changes, React is redrawing way more of the screen than it needs to. It's like repainting your entire house every time you hang a new picture.
Why AI creates this: React's default behavior is to re-render components whenever their parent re-renders. This is usually fine, but AI-generated code often structures components in ways that trigger cascading re-renders. The AI writes code that works, but doesn't think about performance implications.
I've seen apps where typing a single character in a search box caused the entire product grid, navigation, and footer to re-render. The app worked. It was just painful to use.
The fix in human terms: Components should only re-render when their specific data changes, not when unrelated things happen elsewhere in the app.
What You Can Actually Do About It
You have three options, depending on your technical comfort level and timeline.
Option A: Install the Skill (If You Use Claude Code)
If you're using Claude Code, you can install Vercel's best practices as an Agent Skill. This means Claude will automatically apply these rules when writing or reviewing your code.
The skill is available at vercel-labs/agent-skills. Installation instructions are in the repository.
This won't fix existing problems, but it will help prevent new ones.
Option B: Ask Your AI to Review for These Patterns
Even without installing anything, you can prompt your AI tool to look for these specific issues. Try something like:
"Review this component for performance issues. Specifically check for: sequential data fetching that could be parallel, large imports that could be code-split, and unnecessary re-renders from poor component structure."
The AI knows about these patterns. It just doesn't apply them by default unless you ask.
Option C: Get a Professional Performance Audit
If your app is already live and users are complaining, you probably need someone to look at the actual code and identify the specific fixes needed. This is what our Code Health Check does - we assess exactly what's wrong and prioritize fixes by impact.
Sometimes a few hours of expert review can identify problems that would take weeks to find through trial and error.
The Bigger Picture
Vercel releasing this ruleset is actually good news for vibe coders. It means the ecosystem is maturing. The tools are getting smarter. A year ago, AI coding assistants had no concept of React performance patterns. Now they can follow 45 specific rules created by experts at one of the most respected React companies.
This is the pattern we're seeing across AI-assisted development: the tools start by making things possible, then gradually make them better. You were early. Early means you hit problems before the solutions existed. But those solutions are arriving.
The app you built is still valuable. The users you have still matter. The performance issues are fixable. You just need to know what to look for.
Understanding these three patterns - waterfall requests, bundle bloat, and re-render madness - gives you vocabulary for the problems. It helps you ask the right questions, whether you're prompting an AI, hiring a developer, or learning to fix things yourself.
The wall isn't made of stone. It's made of specific, identifiable, solvable problems. And now you know what three of the biggest ones are called.
App feeling sluggish?
Our Code Health Check identifies exactly which performance issues are affecting your users and what it would take to fix them. A few hours of expert review can make your app feel fast again.
