We are not going to build this, because Substack still has no write API. The Developer API they opened in 2026 is read-only (its one documented endpoint returns public profile data for creators who link a LinkedIn handle), and there is no endpoint for creating, publishing or scheduling a Note.
The library linked here, and every other "Substack API" out there, works by replaying a logged-in browser session cookie (substack.sid) against Substack's internal endpoints. That breaks without warning and puts your Substack account at risk, so it is not something we will ship as a platform integration. If Substack publishes an official write API for Notes, we will revisit this. In the meantime the closest thing that works today is scheduling the same short-form text to X, LinkedIn, Threads and Bluesky from a single Zernio post.
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Miquel Palet López
Aug 26
We are not going to build this, because Substack still has no write API. The Developer API they opened in 2026 is read-only (its one documented endpoint returns public profile data for creators who link a LinkedIn handle), and there is no endpoint for creating, publishing or scheduling a Note.
The library linked here, and every other "Substack API" out there, works by replaying a logged-in browser session cookie (
substack.sid) against Substack's internal endpoints. That breaks without warning and puts your Substack account at risk, so it is not something we will ship as a platform integration. If Substack publishes an official write API for Notes, we will revisit this. In the meantime the closest thing that works today is scheduling the same short-form text to X, LinkedIn, Threads and Bluesky from a single Zernio post.