OpenAI key got used by someone else, $412 in one night

They got it from your website. Anything prefixed VITE_ is baked into the JavaScript bundle that every visitor downloads. Open your site, DevTools > Sources, search sk- and you'll find it. Bots crawl for exactly this.

Replit Secrets doesn't help when the frontend reads it, because the build copies the value into public code.

Now:

1. The old key is deleted, good. Check the OpenAI dashboard for other keys/projects you don't recognize.
2. Put the new key only on a server. Smallest possible change: a tiny backend endpoint (Express on the same Repl, or a serverless function) that calls OpenAI, and your React app calls that.

   app.post("/api/chat", requireUser, rateLimit, async (req, res) => {
     const r = await openai.chat.completions.create({
       model: "gpt-4o-mini",          // fixed on the server, not from the client
       messages: req.body.messages.slice(-10),
       max_tokens: 500,
     });
     res.json(r.choices[0].message);
   });

   Note the model and limits are decided server side. Otherwise the endpoint itself becomes a free proxy.
3. Put auth + a per-user rate limit on that endpoint.
4. In OpenAI: use a separate project for this app, set budget alerts, and keep auto-recharge off. With prepaid credits, the balance is effectively your hard cap.

Refund: open a support ticket, explain the key was exposed and show the model mismatch. Not guaranteed but people do sometimes get it back.