> ## Documentation Index
> Fetch the complete documentation index at: https://docs.trynito.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Request format

> JSON bodies, size caps, and multipart uploads.

## JSON Bodies

Send `Content-Type: application/json`. Chat Completions drops unknown fields at gateway-owned objects for compatibility with OpenAI-style clients.

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
curl "https://app.trynito.ai/v1/chat/completions" \
  -H "Authorization: Bearer z_sk_your_key_here" \
  -H "Content-Type: application/json" \
  -d '{ "model": "openai/gpt-5.5", "messages": [{ "role": "user", "content": "Hi" }] }'
```

Bodies are size-capped per route (4 MiB on the non-chat inference routes).

## Multipart Uploads

Chat completions also accept `multipart/form-data`: a `request` part with the JSON body plus image files referenced from the messages as `attachment://<id>`. Limits: 10 files, 5 MiB per image, 50 MiB combined, PNG, JPEG, or WebP, 2048 px long edge. See [Image input](/api/api-reference/multimodal/image-input).

## Related

* [Response format](/api/api-reference/overview/response-format)
* [Error format](/api/api-reference/overview/error-format)


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