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Substack API MCP

Substack does not provide a native public API for publishing posts.

But authors who want to draft, publish, and schedule from AI agents (Cursor, Claude, and other MCP hosts) still need a way out. This is the MCP server to publish to Substack via any agent.

Will not start without a valid APISUBSTACK_API_KEY (ask_*). Get API key here: apisubstack.com.

Why this exists

Reality	What we built
No official Substack write/publish API for authors	A posting MCP so agents can create drafts, publish now, and schedule
Authors live in the browser editor	Authors publish through their agents instead
Session-cookie auth is the practical path today	substack.sid + your publication URL, gated by an API Substack key

Examples

• ignalex.substack.com

Tools

Tool	Description
test_connection	Verify substack.sid and return profile
create_post	Create draft / publish now / schedule (+ optional tags)
get_draft	Fetch draft by id
update_draft	Update draft fields
publish_post	Publish existing draft
schedule_post	Schedule existing draft
delete_draft	Delete draft
list_tags	List publication tags
create_tag	Create tag
set_tags	Ensure + attach tags
get_post_tags	List tags on a post/draft

Install

cd /path/to/Substack-API-MCP
python3 -m venv .venv
source .venv/bin/activate
pip install -e .

Auth env

1. Sign in at apisubstack.com, start the free trial, generate an ask_* API key.
2. Copy your Substack substack.sid cookie:
   • Open Chrome and sign in to Substack.
   • Open DevTools → Application → Cookies.
   • Select https://substack.com (or your publication host, e.g. https://yourname.substack.com).
   • Find the cookie named substack.sid and copy its Value.
3. Export:

export APISUBSTACK_API_KEY="ask_YOUR_KEY"
export SUBSTACK_PUBLICATION_URL="https://yourname.substack.com"
export SUBSTACK_SID="YOUR_SUBSTACK_SID_VALUE"
# optional
# export SUBSTACK_USER_ID="123456"

Cookies expire. If you get 401/403, refresh substack.sid and try again.

Run

substack-api-mcp
# or
python -m substack_api_mcp

Cursor / Claude Desktop config

See mcp.example.json:

{
  "mcpServers": {
    "substack-api": {
      "command": "/ABSOLUTE/PATH/TO/Substack-API-MCP/.venv/bin/substack-api-mcp",
      "args": [],
      "env": {
        "APISUBSTACK_API_KEY": "ask_YOUR_KEY",
        "SUBSTACK_PUBLICATION_URL": "https://yourname.substack.com",
        "SUBSTACK_SID": "YOUR_SUBSTACK_SID_VALUE"
      }
    }
  }
}

Use absolute paths. Restart the host after config changes.

License

Use at your own risk. Not affiliated with Substack. Built so authors can publish through their agents when Substack itself does not offer a native publishing API.