Python Substack

Unofficial Python tools for publishing to Substack.

Features

• Create drafts and publish posts from Python.
• Convert Markdown into Substack's editor document format.
• Upload local images while rendering Markdown.
• Set audience, comment permissions, SEO title, SEO description, slug, sections, and tags.
• Publish now, schedule drafts, or keep drafts unpublished by default.
• Authenticate with email/password, cookies JSON, or a browser cookie string.
• Run a FastMCP server for AI-assisted publishing workflows.

Installation

pip install python-substack

Install the MCP server extra:

pip install "python-substack[mcp]"

Setup

Copy .env.example to .env and fill in one authentication method:

EMAIL=
PASSWORD=
PUBLICATION_URL=
COOKIES_PATH=
COOKIES_STRING=

Use either EMAIL and PASSWORD, or cookie-based authentication with COOKIES_PATH or COOKIES_STRING. Cookie authentication is usually the better option if Substack prompts for captcha or magic-link sign-in.

Newer Substack accounts may only have magic-link sign-in enabled. To set a password, sign out of Substack, choose "Sign in with password", then choose "Set a new password".

Quickstart

import os

from dotenv import load_dotenv
from substack import Api

load_dotenv()

api = Api(
    email=os.getenv("EMAIL"),
    password=os.getenv("PASSWORD"),
    publication_url=os.getenv("PUBLICATION_URL"),
)

result = api.create_draft_from_markdown(
    title="Shipping with Python",
    subtitle="A short note from a script",
    markdown="""
# Hello

This draft was created from **Markdown**.

![Alt text](https://example.com/image.png "Image caption")
""",
    tags=["python", "automation"],
    slug="shipping-with-python",
)

print(result["draft"]["id"])

create_draft_from_markdown creates a draft by default. It only publishes when publish=True is passed.

CLI

Check authentication without creating a draft:

substack-auth-check

With a cookies JSON file:

substack-auth-check --cookies cookies.json

Publish a Markdown file as a draft:

substack-publish-markdown post.md --title "My Post"

Create and publish:

substack-publish-markdown post.md --title "My Post" --publish

Publish from YAML:

substack-publish-yaml draft.yaml

Useful options:

substack-publish-markdown post.md \
  --title "My Post" \
  --subtitle "Optional subtitle" \
  --tag python \
  --tag substack \
  --slug my-post \
  --search-engine-title "SEO title" \
  --search-engine-description "SEO description"

Cookie Authentication

Cookie authentication avoids logging in with email/password on every run and helps when Substack requires captcha or magic-link sign-in.

Use a cookies JSON file:

import os

from dotenv import load_dotenv
from substack import Api

load_dotenv()

api = Api(
    cookies_path=os.getenv("COOKIES_PATH"),
    publication_url=os.getenv("PUBLICATION_URL"),
)

Or paste a browser cookie header into COOKIES_STRING:

import os

from dotenv import load_dotenv
from substack import Api

load_dotenv()

api = Api(
    cookies_string=os.getenv("COOKIES_STRING"),
    publication_url=os.getenv("PUBLICATION_URL"),
)

To get a cookie string:

1. Sign in to Substack in your browser.
2. Open developer tools.
3. Go to the network tab and refresh Substack.
4. Select a request such as subscription/unred/subscriptions.
5. Copy the full cookie request header value into COOKIES_STRING.

To export a working session to a cookies JSON file:

api.export_cookies("cookies.json")

Then set:

COOKIES_PATH=cookies.json

The CLI also accepts a cookie JSON path:

substack-publish-markdown post.md --cookies cookies.json

Low-Level Post Builder

import os

from dotenv import load_dotenv
from substack import Api
from substack.post import Post

load_dotenv()

api = Api(
    email=os.getenv("EMAIL"),
    password=os.getenv("PASSWORD"),
    publication_url=os.getenv("PUBLICATION_URL"),
)

user_id = api.get_user_id()

post = Post(
    title="How to publish a Substack post using Python",
    subtitle="Created with python-substack",
    user_id=user_id,
    audience="everyone",
    write_comment_permissions="everyone",
)

post.paragraph("This is a paragraph.")
post.add(
    {
        "type": "paragraph",
        "content": [
            {"content": "A link to "},
            {
                "content": "Substack",
                "marks": [{"type": "link", "href": "https://substack.com"}],
            },
        ],
    }
)
post.add({"type": "paywall"})
post.add({"type": "captionedImage", "src": "https://example.com/image.png"})

draft = api.post_draft(post.get_draft())
api.prepublish_draft(draft.get("id"))
api.publish_draft(draft.get("id"))

Markdown Support

from substack.post import Post

post = Post("Title", "Subtitle", user_id=1)
post.from_markdown(
    """
# Heading

Paragraph with **bold**, *italic*, `code`, [links](https://example.com), and footnotes.[^1]

- Lists
- Images

![Alt](local-image.png "Caption")

[^1]: Footnote text.
"""
)

Supported Markdown includes headings, paragraphs, bold, italic, inline code, strikethrough, links, images, linked images, image captions, code blocks, blockquotes, ordered lists, unordered lists, horizontal rules, and footnotes.

When an Api instance is passed to from_markdown, local image paths are uploaded before the draft is created:

post.from_markdown(markdown_content, api=api)

YAML Drafts

title: "My Post Title"
subtitle: "My Post Subtitle"
audience: "everyone"
write_comment_permissions: "everyone"
search_engine_title: "SEO title"
search_engine_description: "SEO description"
slug: "my-post-title"
tags:
  - python
  - substack
markdown: |
  # Introduction

  This post body is Markdown.

The lower-level node format is also supported:

title: "My Post Title"
subtitle: "My Post Subtitle"
body:
  0:
    type: "heading"
    level: 1
    content: "Introduction"
  1:
    type: "paragraph"
    content: "This is a paragraph."
  2:
    type: "captionedImage"
    src: "local_image.jpg"

MCP Server

Install the MCP extra:

pip install "python-substack[mcp]"

Run the server over stdio:

substack-mcp

Equivalent Python entry point:

python -c "from substack_mcp.mcp_server import main; main()"

Available tools:

• post_draft_from_markdown(...)
• put_draft(draft_id, update_payload)
• add_tags(draft_id, tags)
• prepublish_draft(draft_id)
• publish_draft(draft_id, send=True, share_automatically=False)

Development

pip install pre-commit
pre-commit install
pytest

Live Substack tests are opt-in. Set RUN_SUBSTACK_E2E=1 and configure credentials before running them.

Release changes are tracked in CHANGELOG.md.

Disclaimer

This project is not affiliated with Substack.