How to Turn the Claude API into a REST Endpoint

If you're searching for this, you probably already have Claude working through Anthropic's SDK or raw HTTPS calls, but you need something more portable: a stable REST endpoint that your own app, your team, or a third-party service can call with a normal API key — without every developer holding your Anthropic credentials.

The short answer: Claude's API is already HTTP-based, but it's designed for direct, authenticated calls with your Anthropic secret key. "Turning it into a REST endpoint" means building (or using) a thin layer in front of it that issues its own application-level keys, forwards requests to Claude, and returns responses in a format your systems can rely on long-term. There are two realistic paths — build the wrapper yourself, or use a hosted gateway like SubToAPI that does it out of the box. Below is how both work.

Why you'd wrap Claude behind your own REST endpoint

Calling Anthropic's API directly works fine for a prototype, but it creates problems once you ship:

• Key exposure risk — every client, server, or teammate that calls Claude directly needs your real Anthropic key, which is hard to rotate or scope.
• No per-app or per-team keys — you can't issue a key to one product or one contractor and revoke just that key later.
• No usage visibility — you don't get a clean breakdown of who used what, in tokens or cost, without building logging yourself.
• Coupling to the SDK — if you want other languages, serverless functions, or no-code tools to call Claude, you need a plain HTTPS interface, not an SDK dependency.

A REST endpoint in front of Claude solves all four: it's just POST requests with your own bearer tokens, independent of which model or SDK sits behind it.

Option 1: Build the wrapper yourself

If you want full control, you can stand up a small proxy service. The pattern is the same regardless of language: your server holds the real Anthropic key, your clients hold a key you issue, and your proxy validates, forwards, and returns.

// server.js — minimal Claude-to-REST wrapper
import express from "express";

const app = express();
app.use(express.json());

const VALID_KEYS = new Set([process.env.APP_KEY_1, process.env.APP_KEY_2]);

app.post("/v1/messages", async (req, res) => {
  const auth = req.headers.authorization?.replace("Bearer ", "");
  if (!VALID_KEYS.has(auth)) {
    return res.status(401).json({ error: "invalid_api_key" });
  }

  const upstream = await fetch("https://api.anthropic.com/v1/messages", {
    method: "POST",
    headers: {
      "x-api-key": process.env.ANTHROPIC_API_KEY,
      "anthropic-version": "2023-06-01",
      "content-type": "application/json",
    },
    body: JSON.stringify(req.body),
  });

  const data = await upstream.json();
  res.status(upstream.status).json(data);
});

app.listen(3000);

This gets you a real REST endpoint, but to make it production-safe you still need to add:

• rate limiting and quota enforcement per key
• streaming passthrough (Server-Sent Events over the proxy, not just JSON)
• structured logging of tokens/cost per key, per team
• key rotation and revocation without redeploying
• retries and failover when Anthropic returns a 5xx or 429

None of this is hard individually, but it's ongoing maintenance for infrastructure that isn't your product.

Option 2: Use a hosted gateway

This is exactly what SubToAPI is for: it sits between your app and Claude, issuing its own sub_live_... keys so you never hand out your Anthropic credentials, and it already handles streaming, tool use, usage metadata, and team seats.

Once you've signed up at /signup and grabbed a key, calling Claude as a REST endpoint looks like this:

curl https://api.subtoapi.app/v1/messages \
  -H "Authorization: Bearer $SUBTOAPI_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "claude-sonnet-4-5",
    "max_tokens": 1024,
    "messages": [
      { "role": "user", "content": "Summarize this ticket in two sentences." }
    ]
  }'

That's a stable, documented endpoint — see /docs/messages for the full request/response schema. Each team member or service gets its own sub_live_... key from the dashboard, so you can revoke access for one integration without touching anything else.

Streaming and tool use through the same endpoint

If your wrapper or product needs token-by-token output, you need to handle SSE correctly, not just buffer the full response. SubToAPI exposes this the same way Anthropic does — set "stream": true — and the implementation details are covered in /docs/streaming.

Tool use (function calling) works the same way: define your tools array in the request body exactly as you would against Anthropic directly, and the endpoint forwards tool call results back in the same turn. See /docs/tools if you're wiring up function calling through the REST layer.

Getting started quickly

If you want to skip building and testing a proxy from scratch, the fastest path is:

1. Sign up at /signup and start the free trial.
2. Generate an application key from the dashboard.
3. Follow /docs/quickstart to send your first request.
4. Check /pricing for Solo (€9), Team (€19/seat), and Scale (€49/seat) if you need multiple keys or seats for a team.

Which approach actually makes sense

| Need | Build it yourself | Use SubToAPI | |---|---|---| | Full infra control | Yes | No | | Live in minutes | No | Yes | | Per-app/team keys | You build it | Built in | | Streaming + tool use | You build it | Built in | | Usage metadata per key | You build it | Built in | | Maintenance burden | Ongoing | None |

If your app is a side project calling Claude once, the DIY proxy is fine. If you're shipping to customers, running a team, or need to revoke a leaked key in seconds instead of redeploying, a hosted REST layer is the more realistic choice.

questions

Does Claude's API already use REST? Yes, Anthropic's API is HTTPS/JSON-based, but it expects your actual Anthropic secret key on every call. "Turning it into a REST endpoint" usually means adding your own authentication layer in front of it so you're not distributing that raw key.

Can I keep using the Anthropic SDK if I wrap the API? On the client side, no — your clients call your new endpoint with plain HTTP and your own key format. On the server side (inside your wrapper), you can still use Anthropic's SDK or raw fetch calls to talk to Claude itself.

Does wrapping Claude in a REST endpoint add latency? A well-built proxy adds a few milliseconds for the extra network hop, which is negligible compared to model generation time. Streaming support matters more for perceived latency than the wrapper itself — see /docs/streaming for how that's handled.