Substack User Activity Feed

Use this endpoint when you need to retrieve a Substack author's public activity feed by username, user ID, or profile URL, especially when you want to filter by a specific activity type (note, post, reply, restack, or like) or paginate through a large history. Prefer this over generic web scraping when you need structured, clean activity data from Substack specifically. It is well-suited for monitoring creator activity, competitive research on newsletter authors, or building content digests from Substack writers.

• Unknown or misspelled username returns empty results or 404-equivalent
• Invalid user_id (non-numeric or non-existent) returns an error
• Requesting more pages than available returns a partial result set (early stop)
• Private or deleted Substack profiles may return no results
• Rate limiting or payment failure returns a 402 or error response
• Providing none of username, user_id, or url causes a validation error