Substack API MCP

Claude + Substack

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

Sign in at apisubstack.com, start the free trial, generate an ask_* API key.
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.
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.

Substack Posting MCP

Documentation