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

# Introduction

> PromptStream API overview and authentication

<Note>
  This section introduces the core PromptStream REST API for prompt
  management, experimentation, and usage tracking.
</Note>

## Welcome to the PromptStream API

The PromptStream API lets you version prompts, run A/B experiments, track outcomes, and meter usage—all via simple HTTP endpoints.

We use an **OpenAPI specification** to define every route and model.

## Authentication

All endpoints require your organisation’s API key in an HTTP header:

```http theme={null}
X-API-Key: YOUR_PROMPTSTREAM_API_KEY
```