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How to Protect Your LLM API Key from Frontend Leaks

Building an AI-powered app is exciting, but it comes with a major security challenge: where do you store your API keys? If you're building a client-side application (React, Svelte, Vue, mobile), putting your OpenAI or Anthropic API key directly in your frontend code is a recipe for disaster.

The Danger of Client-Side API Calls

It's tempting to initialize the OpenAI SDK directly in your browser code to get a prototype running quickly. It works, but it exposes your secret API key to anyone who visits your website.

Hackers use automated bots to scrape GitHub repositories and public websites looking for strings that start with sk-. Once they find your key, they can:

  • Drain your bank account: They can use your quota to power their own apps or resell access.
  • Get you banned: OpenAI and other providers will revoke keys and ban accounts that show suspicious activity.
  • Access private data: If you're using fine-tuned models, they might gain unauthorized access.

The Traditional Solution: Build a Backend

The standard advice is to "move it to the backend." You create a server (Node.js, Python, Go) that holds the secret key. Your frontend talks to your backend, and your backend talks to OpenAI.

This works, but it introduces significant friction:

  • You have to build, host, and maintain a server.
  • You need to implement authentication to ensure only your users can call the endpoint.
  • You need to handle rate limiting to prevent abuse.
  • If you want to charge users, you have to build a billing system and credit tracking logic.

Suddenly, your "simple wrapper around OpenAI" has turned into a full-stack engineering project.

The Modern Solution: Use a Smart Proxy

This is exactly why we built PromptProxy. It acts as a secure middleware between your frontend and LLM providers. Instead of building your own backend infrastructure, you simply route your requests through our secure proxy.

How It Works

PromptProxy sits in the middle. You give us your API keys (stored securely), and we give you a public-safe endpoint to use in your frontend.

Here is how simple the migration is:

Security Benefits

  1. Hidden Credentials: Your actual OpenAI/Anthropic keys never leave our secure vault. The client only sees a PromptProxy key which is useless without a valid user JWT.
  2. User Authentication: We integrate with your existing auth provider (Firebase, Supabase, Auth0, Clerk). We verify the user's identity before forwarding any request.
  3. Rate Limiting & Fraud Protection: We automatically block abusive IP addresses and enforce rate limits per user, protecting your wallet from runaway loops or malicious attacks.

Conclusion

Security shouldn't be an afterthought, but it also shouldn't block you from shipping. By using a proxy service, you can keep your frontend code clean and your API keys secure, without the overhead of maintaining a custom backend.

Ready to secure your AI app? Get started with PromptProxy for free and stop worrying about API key leaks.