> ## Documentation Index
> Fetch the complete documentation index at: https://docs.correl8.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# API overview

> Correl8 REST API for custom integrations

The REST API is for **custom integrations** that cannot use MCP. For AI agents, use [MCP](/essentials/mcp) instead.

## Base URL

```
https://api.correl8.ai
```

## Authentication

Project API keys from **Settings**. Send as:

```bash theme={null}
Authorization: ApiKey c8.xxx
```

```bash theme={null}
X-Api-Key: c8.xxx
```

Keys are scoped to a single project — a key for project A returns `404` on project B.

## Endpoints

| Method | Path                                                            | Description                                                       |
| ------ | --------------------------------------------------------------- | ----------------------------------------------------------------- |
| `GET`  | `/v1/project/{project_id}/correl8-guidelines/`                  | Project guidelines (same as MCP tool `get_correl8_guidelines`)    |
| `GET`  | `/v1/project/{project_id}/research/studies/`                    | Active studies for a user (same as MCP tool `get_active_studies`) |
| `POST` | `/v1/project/{project_id}/observations/`                        | Create one or more observations                                   |
| `POST` | `/v1/project/{project_id}/research/studies/{study_id}/answers/` | Post a research study answer                                      |

## Free tier limits

**1,000 processed observations per month** per workspace. When the limit is reached, Correl8 keeps ingesting but does not run tag matching or issue digest. Check usage in **Settings**.

## Error responses

| Status | Meaning                                  |
| ------ | ---------------------------------------- |
| `400`  | Validation error                         |
| `401`  | Missing or invalid API key               |
| `404`  | Project not found, or key not authorized |