Substack Publisher

Substack Publisher

Publish markdown posts to Substack as drafts or newsletter articles. Converts markdown to Substack's ProseMirror JSON format.

Requirements

Set these environment variables (add to .env):

• SUBSTACK_SID - Your substack.sid session cookie value
• SUBSTACK_SUBDOMAIN - Your Substack subdomain (e.g., adrianpetcu)
• SUBSTACK_USER_ID - Your Substack user ID (e.g., 106993810)

Quick Start

python scripts/publish_to_substack.py posts/daily-thoughts/03-context-driven-bug-fixing.md --dry-run

Script Usage

python scripts/publish_to_substack.py <file.md> [options]

Required:

• file - Path to the markdown post file

Options:

• --title - Override post title (default: extracted from # heading)
• --subtitle - Override subtitle (default: extracted from ## Hook section)
• --publish - Publish immediately instead of creating a draft
• --audience - Post audience: everyone (default) or paid
• --dry-run - Output ProseMirror JSON to stdout without making API calls

Workflow

1. Select the post file - Choose a markdown post from the repository
2. Preview with dry-run - Always run --dry-run first to verify the conversion
3. Create draft - Run without --publish to create a draft on Substack
4. Review in Substack - Open the draft URL and verify formatting
5. Publish - Either publish from Substack's editor or re-run with --publish

Markdown Format Support

The script handles the repository's post template format:

• Title: Extracted from the first # heading
• Subtitle: Extracted from the ## Hook section content
• Body: All remaining sections converted to ProseMirror nodes

Included sections: Key Points, Body Outline, Call to Action, Visual Walkthrough, and any custom sections.

Excluded sections (metadata): Status, Hashtags, Notes, Verdict, LinkedIn Assessment.

Block elements: Paragraphs, headings (H1-H3), bullet lists, ordered lists, code blocks (with language), blockquotes, horizontal rules, images (HTTP URLs only).

Inline marks: bold, italic, code, links.

Special handling: Bold labels on standalone lines (e.g., **Section Name:**) become H3 headings. Local image paths are skipped with a warning.

Examples

Preview conversion:

python scripts/publish_to_substack.py posts/daily-thoughts/03-context-driven-bug-fixing.md --dry-run

Create a draft:

python scripts/publish_to_substack.py posts/daily-thoughts/03-context-driven-bug-fixing.md

Publish with custom title:

python scripts/publish_to_substack.py posts/daily-thoughts/03-context-driven-bug-fixing.md \
  --title "How AI Turns Vague Bugs Into Actionable Tickets" --publish

Paid subscribers only:

python scripts/publish_to_substack.py post.md --audience paid

How to Get SUBSTACK_SID

1. Log into Substack in your browser
2. Open DevTools (F12) → Application → Cookies
3. Find substack.sid cookie for your subdomain
4. Copy the value and set it: export SUBSTACK_SID="your-cookie-value"

Alternatively, inspect any network request in DevTools → Headers → Cookie and copy the substack.sid=... value.

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