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

# Usage & Limits

> API request limits and intended usage guidelines.

## Intended Use

This API is intended exclusively for:

* Content owners accessing their own Substack publication data
* Applications authorized by publication owners to interact with their content
* Legitimate integrations with Substack publications by copyright holders

<Warning>
  This API is not intended for:

  * Unauthorized scraping of Substack content
  * Accessing publications without explicit permission from the content owner
  * Mass collection or aggregation of Substack content without authorization
</Warning>

Violation of these usage guidelines may result in immediate API access termination.

## Rate Limits

| Endpoint      | Rate Limit             |
| ------------- | ---------------------- |
| /posts/latest | 10 requests per minute |
| /posts/top    | 10 requests per minute |
| /posts/search | 20 requests per minute |
| /post         | 15 requests per minute |

* Production API keys use the limits shown above, while test API keys are limited to 3 requests per minute for all endpoints.
* Rate limits are tracked by the **client's IP address**, not by API key.
* Exceeding these limits will result in a `429 Too Many Requests` response.

## Authentication

<Info>
  Authentication is handled via the `X-API-Key` header. Each API key is linked to one Substack publication and can only access its data.
</Info>

### API Key Format

* Production keys start with `sk_live_`
* Test keys start with `sk_test_`

### Using Your API Key

Include your API key in all requests using the `X-API-Key` header:

```bash
curl https://api.substackapi.dev/api_key/validate \
-H "X-API-Key: sk_live_your_key_here"
```