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API Direct – Substack User Posts
x402
API Direct – Substack User Posts is a paid API for AI agents from x402.apidirect.io, paid per call via x402, $0.004/call, status unknown (last checked 2026-10-30).
Retrieves all posts by a Substack author across their publications, sorted newest first, with optional AI sentiment analysis.
Price / call$0.004
Success—
StatusUnknown
How this service works
Get an author's posts across all their publications, newest first.
Output
Returns a paginated list of posts (up to 50 per page) from all of the author's Substack publications, sorted newest first. Each post includes metadata such as title, publication date, publication name, and post URL. When sentiment analysis is enabled, each post also includes Plutchik's Wheel emotion scores, dominant emotion, intensity rating, and polarity (positive/negative/neutral).
Example use cases
Research a newsletter writer's output
“I'm evaluating whether to hire a writer — can you fetch the last 2 pages of Substack posts by the author at https://substack.com/@packyM and tell me how many they've published and what the overall tone is? Include sentiment analysis.”
Monitor a Substack author's latest articles
“What are the newest posts published by the Substack user with ID 123456? Just grab the first page so I can see what they've written recently.”
Competitive content analysis for a newsletter
“I want to analyze the writing style and emotional tone of all posts from the Substack author 'stratechery' — pull 5 pages of their posts with sentiment scores included so I can compare their content strategy to mine.”
Technical details
Endpoint
GEThttps://x402.apidirect.io/v1/substack/user/posts?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need to retrieve post history for a specific known Substack author by username, numeric ID, or profile URL — especially when you want multi-publication aggregation or AI-powered sentiment/emotion analysis per post. Prefer it over general Substack search endpoints when you already know the author identity and want their actual content rather than author discovery.
Side effects
- Invalid or non-existent username/user_id/url returns an error or empty result set
- No identifier provided (username, user_id, or url all missing) causes a validation error
- Pages parameter exceeding 60 results in a schema validation error
- Author has no posts, returning an empty list
- Rate limiting or upstream Substack API unavailability causes request failure
- Malformed profile URL format returns an error
- Payment failure (insufficient USDC balance) blocks the request
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object |
Tags
x402
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