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

Examples

• ignalex.substack.com

Tools

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:

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

Attribution-or-Royalty (source available). See `LICENSE` and `COMMERCIAL_LICENSE.md`.

• Non-commercial use: allowed (keep copyright + license notice).
• Commercial use: either visible attribution everywhere the software is used, or a paid royalty / commercial license via apisubstack.com.

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.