Schedule Substack posts from Markdown drafts

1. In the Substack publisher dashboard, click Create and select Article, then paste the text into the editor.
2. Substack says its post editor does not support Markdown, so headings, bold text, links and lists written in Markdown have to be redone with the editor toolbar, and images uploaded again.
3. Click Continue, choose the audience, who can comment and whether to send via email and the Substack app inbox, then check "Schedule time to email and publish" and pick a date and time.
4. To promote the post, open Create > Note after it goes live, or schedule the Note with the calendar icon in the Notes composer.
5. The formatting pass repeats for every issue, and a wrong time zone or a missed audience setting only shows up once subscribers already have the email.

Turn essay.md into a Substack draft for everyone, schedule it for Tuesday 8:00 New York time, and schedule a Note with a link card to it for 12:00 the same day.

1. 01

   Read the file and keep its structure

   The agent takes the first heading as the title and an optional subtitle line, and sends the rest as Markdown to create_draft. Local image paths cannot be used, so it asks for hosted image URLs or leaves a placeholder and names it in the report.

2. 02

   Check the calendar before picking the slot

   list_posts with status scheduled shows what is already queued. When another issue is set for the same day, the agent stops and asks instead of stacking two emails on one morning.

3. 03

   Pin the time zone

   The Substack web form uses the time zone of your device clock. The agent always sends an explicit offset, refuses a time in the past, and refuses a date more than three months out, the furthest Substack lets a post be scheduled.

4. 04

   Warn about length before sending

   A very long issue with many images can be clipped by Gmail. The agent flags a draft that looks close to that size, so you can split it or trim images before the send is locked in.

5. 05

   Schedule the email, then the Note

   schedule_post waits for your OK and returns the edit link, so you can open the draft in Substack first. The Note goes out with publish_at a few hours after the post, so the link card points to a post readers can already open.

Draft created: "Why we stopped shipping on Fridays" (post 148420031), audience everyone
2 images placed from URLs, 1 placeholder left: diagram.png has no hosted URL
No other post scheduled on Tue 14 Oct
Scheduled: Tue 14 Oct 2026, 08:00 America/New_York, web + email
Note scheduled: Tue 14 Oct, 12:00, link card to the post
Edit link: https://yourname.substack.com/publish/post/148420031

• Substack lets a post be scheduled at most three months ahead, and only from the web editor; the Substack app cannot schedule articles, podcasts or video posts.
• Substack emails a post only once. Edits made after the send show on the web and in the Substack app, and the email cannot be sent again.
• Gmail clips emails larger than about 102KB, and the Substack editor counts links, images and the text your publication adds to the top or bottom of every email toward that size. Posts over 1,000,000 characters cannot be saved at all.
• Substack Notes are not emailed to subscribers; they may surface in a notes roundup digest or a push notification instead.

schedule_post and publish_note ask for your OK by default. To run it weekly without you, switch confirmation off for those tools in your dashboard.

Sources: Substack: Do you support Markdown? · Substack: How do I publish a new post on Substack? · Substack: How do I schedule an article to publish for a future date? · Substack: Why does it say "Your post may be truncated"? · Substack: Getting started on Substack Notes · Substack: Guide to your Substack Posts page

curl https://cotlet.dev/api/v1/substack/schedule_post \
  -H "Authorization: Bearer $COTLET_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"post_id":"148420031","publish_at":"2026-10-14T08:00:00-04:00","send_email":true}'

{
  "post_id": "148420031",
  "status": "scheduled",
  "publish_at": "2026-10-13T08:00:00-04:00",
  "audience": "everyone",
  "url": "https://yourname.substack.com/p/notes-on-pricing"
}

MCP: add https://cotlet.dev/mcp/v1 with the same key; the tool is substack_schedule_post. Example data.

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