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

# API Overview

> Interface specifications and routing conventions for ONR.

Open Next Router is fundamentally designed to provide an **OpenAI-compatible** surface area for any downstream client, while managing the complexity of routing those requests to arbitrary providers behind the scenes.

## Core API Contract

Clients interacting with ONR should generally assume they are talking to a standard OpenAI completion, chat, or embedding endpoint. ONR sits in the middle and parses the standard shape:

* `POST /v1/chat/completions`
* `POST /v1/embeddings`
* `GET /v1/models`

## Dynamic Provider Override

Normally, ONR picks which upstream provider to route to by looking at the `model` parameter inside the JSON body and matching it against your `models.yaml` registry.

However, a client can explicitly force a request to hit a specific upstream provider using the custom override header:

```http theme={null}
x-onr-provider: anthropic
```

*If present, this header bypasses `models.yaml` entirely and executes the DSL defined in `config/providers/anthropic.conf`.*

## Streaming Guarantee

Streaming LLM responses is notoriously tricky due to varying Server-Sent Event (SSE) framings, chunk layouts, and closing signals across different LLM providers.

ONR guarantees that if a client sends a standard OpenAI `stream: true` flag in the JSON body:

1. It will establish a persistent `text/event-stream` with the client.
2. It will apply the respective `sse_parse` transformations defined in the provider's DSL.
3. It will emit cleanly formatted, OpenAI-schema-compliant delta chunks back to the client.