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