Publish Substack Article

Publish Markdown content to Substack post editor, converting Markdown to HTML and pasting as rich text. Saves as draft for user review before publishing.

Prerequisites

Browser automation MCP (either one):
- Chrome DevTools MCP (mcp__chrome-devtools__*)
- Playwright MCP (mcp__playwright__*)
User logged into Substack
Python 3 with markdown package (pip install markdown)
copy_to_clipboard.py script (shared from publish-zsxq-article skill)

Browser MCP Tool Mapping

This skill works with both Chrome DevTools MCP and Playwright MCP. Use whichever is available:

Action	Chrome DevTools MCP	Playwright MCP
Navigate	`navigate_page`	`browser_navigate`
Take snapshot	`take_snapshot`	`browser_snapshot`
Take screenshot	`take_screenshot`	`browser_take_screenshot`
Click element	`click`	`browser_click`
Fill text	`fill`	`browser_type`
Press key	`press_key`	`browser_press_key`
Evaluate JS	`evaluate_script`	`browser_evaluate`

Detection: Check available tools at runtime. If mcp__chrome-devtools__navigate_page exists, use Chrome DevTools MCP. If mcp__playwright__browser_navigate exists, use Playwright MCP.

Key URLs

Substack dashboard: https://{publication}.substack.com/publish
Post editor: https://{publication}.substack.com/publish/post/{postId}
Default publication: verysmallwoods

Editor Interface

The Substack post editor uses Tiptap (ProseMirror-based WYSIWYG editor).

Key Elements

Title input: textbox "title" (placeholder: "Title")
Subtitle input: textbox "Add a subtitle…"
Content area: .ProseMirror (Tiptap editor, "Start writing...")
Save status: button "Saved" (auto-saves)
Preview button: button "Preview"
Continue button: button "Continue" (publish flow - DO NOT USE)
Settings sidebar: button "Settings" (title, description, thumbnail)

Settings Sidebar (left panel)

When "Settings" or "File Settings" is open:

Title: textbox "Add a title..."
Description: textbox "Add a description..."
Thumbnail: Upload button (3:2 aspect ratio)

Toolbar

Bold, Italic, Strikethrough, Code, Link, Image, Audio, Video, Quote, Lists (bullet/ordered), Button, More (Code block, Divider, Footnote, LaTeX, etc.)

Content Insertion Method

CRITICAL: Use clipboard paste with HTML content, NOT direct fill or plain Markdown paste.

The Tiptap editor handles HTML paste natively and renders it as rich content. The workflow is:

Convert Markdown to HTML using Python's markdown library
Copy HTML to system clipboard using copy_to_clipboard.py html
Focus the editor content area
Press Cmd+V (macOS) or Ctrl+V (Windows/Linux) to paste

Why HTML paste?

fill tool → Content treated as plain text, no formatting
Plain Markdown paste → Tiptap does NOT parse Markdown on paste
HTML paste → Tiptap renders HTML as rich content (headings, code blocks, links, bold, etc.)

Known limitation: Substack's editor does NOT support HTML tables. Tables will be collapsed into plain text. See Step 0: Pre-Processing for converting tables to images.

Main Workflow

Step 0: Pre-Processing — Convert Tables to Images

Substack does NOT render HTML tables. They collapse into plain text. Any Markdown table must be converted to a PNG image and uploaded separately.

Workflow:

Detect tables in the Markdown file (lines with | forming table structure)
Create styled HTML for each table:

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<style>
body { font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif; margin: 0; padding: 20px; background: white; }
table { border-collapse: collapse; width: 100%; font-size: 15px; line-height: 1.6; }
th { background: #f8f8f8; font-weight: 600; text-align: left; padding: 10px 16px; border-bottom: 2px solid #e0e0e0; }
td { padding: 8px 16px; border-bottom: 1px solid #eee; }
tr:hover { background: #fafafa; }
code { background: #f0f0f0; padding: 2px 6px; border-radius: 3px; font-size: 13px; font-family: 'SF Mono', Menlo, monospace; }
</style>
</head>
<body>
<table>
<!-- table content here -->
</table>
</body>
</html>

Render to screenshot: Open the HTML file in a browser tab, take a screenshot, close the tab:

# Open HTML in new tab
browser_navigate or new_page: file:///tmp/table1.html

# Take screenshot
browser_take_screenshot: filename=/tmp/table1.png, fullPage=true

# Close tab and return to editor
browser_tabs: action=close

Note the position of each table in the article for later insertion (after which heading/paragraph)
Remove table Markdown from the content before HTML conversion (so it won't appear as plain text in the pasted content)

Image upload happens after pasting the main content — see Step 7.

Step 1: Prepare Content

Read the Markdown file and extract:

Title: from YAML frontmatter title field, or H1 header # Title, or filename
Subtitle: from YAML frontmatter excerpt or description field
Content: full Markdown body (strip YAML frontmatter and any cross-reference links)

Step 2: Convert Markdown to HTML

Use Python's markdown library with tables and fenced_code extensions:

import markdown
import re

with open('/path/to/article.md', 'r') as f:
    content = f.read()

# Strip YAML frontmatter
content = re.sub(r'^---\n.*?\n---\n', '', content, flags=re.DOTALL)

# Strip cross-reference links (e.g., English version link)
# Adjust pattern as needed for your articles
content = re.sub(r'^> .* available at.*\n\n?', '', content, flags=re.MULTILINE)

# Convert to HTML
html = markdown.markdown(content, extensions=['tables', 'fenced_code'])

# Write to temp file
with open('/tmp/substack_article.html', 'w') as f:
    f.write(html)

IMPORTANT: Do NOT use nl2br extension - it converts single newlines to <br> tags, causing extra line breaks in the editor.

Step 3: Navigate to Substack

Navigate to the Substack dashboard and create a new post:

# Navigate to Substack dashboard
navigate to: https://verysmallwoods.substack.com/publish

If not logged in, prompt user to log in:

请先登录 Substack，登录完成后告诉我。
Please log in to Substack first, then let me know.

Step 4: Create New Post

From the dashboard, create a new text post:

Click "Create new" in the sidebar
Select "Text post" (or navigate directly to a new post URL)

Alternatively, if the editor is already open with an empty post, proceed directly.

Step 5: Fill Title and Subtitle

Click the title textbox (textbox "title")
Type the article title
Click the subtitle textbox (textbox "Add a subtitle…")
Type the subtitle/excerpt

click: title textbox
fill/type: article title

click: subtitle textbox
fill/type: article subtitle

Step 6: Insert HTML Content (via Clipboard Paste)

CRITICAL: Do NOT use fill tool - it inserts plain text without formatting.

Copy HTML to system clipboard:

python3 /path/to/copy_to_clipboard.py html --file /tmp/substack_article.html

Click the editor content area (.ProseMirror or paragraph element inside it)
Press Cmd+V to paste:

press_key: Meta+v  (macOS)
press_key: Control+v  (Windows/Linux)

This triggers Tiptap's HTML paste handler, which renders the content as rich text with proper formatting.

Step 7: Insert Table Images

If the article had tables converted to images in Step 0, insert them now:

Navigate to the correct position in the editor — click on the paragraph or empty line where the table should appear (after the relevant heading/text)
Click the Image toolbar button (button "Image") — a dropdown menu appears with options: Image, Gallery, Stock photos, Generate image
Click "Image" menuitem from the dropdown — a file chooser dialog opens
Upload the image via file chooser:
- Playwright MCP: browser_file_upload with the image path
- Chrome DevTools MCP: upload_file with the image path

Important notes:

File path restriction: Playwright MCP only allows file uploads from within allowed roots (project directories). If your image is in /tmp/, copy it to the project directory first
Repeat for each table: Position cursor at the correct location, then upload each table image
Delete residual text: If table content was pasted as plain text (because it wasn't removed in pre-processing), select it (triple-click to select paragraph) and delete before inserting the image

Step 8: Verify Draft

After pasting:

Check the "Saved" status indicator (green dot + "Saved" text)
Take a snapshot to verify content structure
Optionally take a screenshot for visual verification

The editor auto-saves, so no explicit save action is needed.

Step 9: Report Completion

草稿已保存到 Substack。请在 Substack 中预览并手动发布。
Draft saved to Substack. Please preview and publish manually.

Post URL: https://verysmallwoods.substack.com/publish/post/{postId}

Complete Example Flow

User: "把 /path/to/my-article.md 发布到 Substack"

0. Pre-process tables (if any)
   - Detect Markdown tables
   - Create styled HTML for each table
   - Render to screenshots (open in browser, screenshot, close tab)
   - Remove table Markdown from content
   - Note insertion positions

1. Read /path/to/my-article.md
   - Extract title from frontmatter or H1
   - Extract subtitle from frontmatter excerpt
   - Get full Markdown content (with tables removed)

2. Convert Markdown to HTML
   - Strip frontmatter
   - Use markdown.markdown() with ['tables', 'fenced_code']
   - Write to /tmp/substack_article.html

3. Navigate to Substack dashboard or new post

4. Check if logged in
   - If not, prompt user to login

5. Fill title and subtitle

6. Copy HTML to clipboard + Paste
   - python3 copy_to_clipboard.py html --file /tmp/substack_article.html
   - Click editor content area
   - Press Cmd+V

7. Insert table images at correct positions
   - For each table: click position → Image button → Image menuitem → file upload

8. Verify draft saved
   - Check "Saved" status

9. Report success
   - "草稿已保存，请手动预览并发布"

Critical Rules

NEVER click "Continue" - This starts the publish flow. Only save as draft (auto-save handles this)
Always convert to HTML first - Plain Markdown will not be parsed by the Tiptap editor
Use clipboard paste - The only reliable way to insert formatted content
Check login status - Prompt user to login if needed
Preserve original file - Never modify the source Markdown file
Report completion - Tell user the draft is saved and needs manual review
No nl2br extension - Causes double line breaks
Tables → images - Pre-process tables before pasting content; upload images after paste
Playwright file paths - Playwright MCP restricts file uploads to allowed roots; copy temp files to project directory before uploading

Troubleshooting

Content Shows as Plain Text (No Formatting)

If you see raw HTML tags or unformatted text:

Cause: Content was inserted using fill tool instead of clipboard paste
Solution: Use the copy_to_clipboard.py + Cmd+V method (see Step 6)

Tables Not Rendering (Shows Plain Text)

Substack's Tiptap editor does not support HTML tables. They collapse into inline plain text.

Solution: Convert tables to styled HTML → render as screenshots → upload as images (see Step 0 and Step 7)
Alternative: Restructure simple tables as formatted lists
If plain text already pasted: Triple-click the plain text paragraph to select it, press Backspace to delete, then insert the table image at that position

Login Required

If page shows login prompt:

请先登录 Substack: https://verysmallwoods.substack.com
登录完成后告诉我。

Editor Not Loading

If editor elements are not visible:

Wait for page to fully load
Take a new snapshot
If still not loading, refresh the page

Clipboard Copy Fails

If copy_to_clipboard.py fails:

Ensure dependencies: pip install pyobjc-framework-Cocoa (macOS)
Check the HTML file exists and is readable
Try copying a smaller test string first

Element Reference

Element	Selector/Identifier	Description
Title input	`textbox "title"`	Post title
Subtitle input	`textbox "Add a subtitle…"`	Post subtitle
Content area	`.ProseMirror` (Tiptap editor)	Post content
Save status	`button "Saved"`	Auto-save indicator
Preview button	`button "Preview"`	Preview post
Continue button	`button "Continue"`	DO NOT USE - starts publish flow
Settings button	`button "Settings"`	Open settings sidebar
Exit button	`button "Exit"`	Exit editor
Image button	`button "Image"`	Opens image upload dropdown
Image menuitem	`menuitem "Image"`	Opens file chooser for image upload
Author button	`button "{PublicationName}"`	Author/publication selector

Technical Details

Editor Stack

Tiptap: A headless, framework-agnostic rich-text editor built on ProseMirror
ProseMirror: The underlying rich-text editing framework
Paste handling: Tiptap natively parses HTML from clipboard and converts to its internal document model

Content Conversion Pipeline

Markdown file
    ↓ (Python markdown library)
HTML string
    ↓ (copy_to_clipboard.py)
System clipboard (text/html + text/plain)
    ↓ (Cmd+V keyboard shortcut)
Tiptap ProseMirror editor
    ↓ (auto-save)
Substack draft

Supported Formatting

The following Markdown elements are correctly rendered after HTML conversion and paste:

Markdown Element	Substack Support	Notes
Headings (H2-H6)	Yes	H1 not recommended (title is separate)
Bold / Italic	Yes
Inline code	Yes
Code blocks	Yes	Syntax highlighting may vary
Links	Yes
Blockquotes	Yes
Bullet lists	Yes
Ordered lists	Yes
Horizontal rules	Yes
Tables	No → Image	Convert to styled HTML, screenshot, upload as image
Images	Manual	Upload via Image toolbar button → file chooser

publish-substack-article