OpenAI-compatible API guide
How to Test an OpenAI-Compatible API
To test an OpenAI-compatible API, check whether it supports model listing, chat completions, streaming responses, OpenAI-style payloads, and acceptable latency before you use it in an app or buy credits.
Why This Check Matters
Many relays, gateways, and proxy services say they are OpenAI-compatible. In practice, compatibility can be partial: a normal chat request may work while streaming fails, the model list may be missing, or the response shape may not match what OpenAI client libraries expect.
A quick health check helps you find these issues before you connect the endpoint to a product, agent workflow, or long-running script.
Steps to Test an Endpoint
- Confirm the base URL. Use the API root, such as
https://api.example.com/v1, not a dashboard or register page. - Check
/v1/models. Make sure the endpoint can return a model list or at least accept the selected model id. - Send a chat completion. Verify that a normal request returns a 2xx JSON response with a
choicesarray. - Test streaming. Send the same request with
stream: trueand look for server-sent event chunks. - Measure latency and TTFT. Compare normal response latency with time to first streamed token.
- Inspect model behavior. Use a few control questions to catch obvious route or model-family mismatches.
What the Checker Looks For
| Check | What it means | Good result |
|---|---|---|
| Models endpoint | Can the API list available models or accept the selected model? | HTTP 200 and an OpenAI-style model payload |
| Chat completion | Can it answer a normal request? | A JSON response with choices[0].message.content |
| Streaming | Does stream: true return event-style chunks? |
Chunks that arrive as data: events |
| Latency | How long does the first normal response take? | Lower is better and repeated tests should be stable |
| TTFT | How long until the first streamed token appears? | Fast first-token time without proxy buffering |
| Response shape | Will OpenAI SDK-style code understand the response? | Expected fields such as choices, message, and usage tokens |
Run the Check
Paste your API base URL, enter a low-scope test key, choose a model, then run the checker. The tool does not store your API key; it is used only for the live request in your current test.
FAQ
What is an OpenAI-compatible API?
It is an API that follows common OpenAI endpoint paths and payload shapes, so OpenAI client libraries can often connect to it with a custom base URL.
Is OpenAI-compatible the same as official OpenAI?
No. A relay, proxy, or gateway can be compatible with OpenAI request formats without being an official OpenAI service.
Why does streaming fail even when chat works?
Some providers implement normal chat completions but do not correctly support server-sent event streaming, or a proxy buffers the stream until the full response is ready.
Do I need an API key to test it?
For a real endpoint test, yes. You can use a temporary or low-scope test key. You can also try the demo mode first to see what the result looks like.
Can this prove a provider is reliable?
No single test can prove long-term reliability. Use it as a technical health check, then repeat tests over time before relying on a provider.