What does this error code mean?

The server is working, but there’s nothing at that address. The page, file or API route doesn’t exist where the link points. Common causes: a typo, a page that moved without a redirect, a file in the wrong folder in Next.js, or a Vite/React app on Netlify or Vercel with no rewrite to index.html. See 404 in detail.

Your server code crashed while handling the request. The message is vague on purpose; the real error is in your server logs (in Vercel: your project, then Logs). The most common cause is an env var that’s set in .env.local but missing in production. See 500 in detail.

Your host or proxy (Vercel, Cloudflare, Netlify, Nginx) asked your app for the page and got a broken answer or none at all. The middleman is fine; your app behind it crashed, is down, or listens on the wrong port. See 502 in detail.

The server understood the request and still said no: you’re not allowed to see or do this. In Supabase it’s usually a Row Level Security policy; on Cloudflare a firewall rule; on Vercel preview links, Deployment Protection. See 403 in detail.

Too many requests were sent in a short time, so the server is refusing for a while. With AI APIs it means you hit your rate limit or usage tier. In your own app, look for a useEffect that fetches in a loop. See 429 in detail.

A 4xx code means the request was the problem: wrong address, not logged in, not allowed, bad data. A 5xx code means the server was the problem: it crashed, timed out, or is down. 4xx: look at what was sent. 5xx: look at the server logs.

Both come from the host in front of your app. 502 means your app sent back a broken answer or crashed. 504 means your app was too slow and the host gave up waiting. A 504 is usually a slow AI call or database query.

Yes. Every code has its own link, like darnly.dev/tools/http-status-explainer/#502, and Vercel errors too, like #FUNCTION_INVOCATION_TIMEOUT. Use “Copy link” on any code.