Slackfmt Firefox

• Chromium/Chrome: Uses org.chromium.web-custom-data clipboard type
• Firefox: Uses org.mozilla.custom-clipdata clipboard type

We explored various approaches to convert the slackfmt CLI's output to Firefox's format:

• ✗ Direct clipboard format conversion (Swift/Python) - binary format proved difficult
• ✗ Playwright's Clipboard API - ClipboardItem not available in automation context
• ✓ slackfmt web app - Uses JavaScript's Clipboard API which automatically creates the correct format for the browser

This skill is a stopgap solution until we can implement a proper command-line conversion tool. For now, it automates the slackfmt web workflow using Playwright Firefox.

Instructions

Phase 1: Get Markdown Content

1. If $ARGUMENTS is provided and is a file path, read the file
2. If $ARGUMENTS is provided but is not a file path, treat it as markdown content directly
3. If no $ARGUMENTS, read from stdin (check if stdin is available)
4. Store the markdown content for use in Phase 2

Phase 2: Navigate to slackfmt Web App

Using the Playwright Firefox MCP tools:

1. Navigate to https://slackfmt.labs.caue.dev/

   mcp__playwright-firefox__browser_navigate(url: "https://slackfmt.labs.caue.dev/")
   

2. Wait for the page to load and take a snapshot to get element references

   mcp__playwright-firefox__browser_snapshot()
   

3. Locate the markdown input textarea (look for textbox "Markdown input" in the snapshot)

Phase 3: Fill Markdown and Copy

1. Type the markdown content into the textarea using the ref from the snapshot:

   mcp__playwright-firefox__browser_type(
     ref: "<textarea-ref>",
     element: "Markdown input textbox",
     text: "<markdown-content>"
   )
   

2. Take another snapshot to locate the "Copy" button

3. Click the "Copy" button using its ref:

   mcp__playwright-firefox__browser_click(
     ref: "<copy-button-ref>",
     element: "Copy button"
   )
   

Phase 4: Confirm Success

Tell the user:

✓ Copied to clipboard! The markdown has been converted to Slack's format and is ready to paste.

Paste into Slack now - you should see native Slack bullets with proper nesting and formatting.

Phase 5: Clean Up

Close the browser:

mcp__playwright-firefox__browser_close()

Example

# From a file
/slackfmt-firefox /tmp/scrum-update.md

# From stdin
cat notes.md | /slackfmt-firefox

# Inline markdown
/slackfmt-firefox "- **Bold item**\n  - Nested item with [link](https://example.com)"

Notes

• The slackfmt web app processes everything client-side - your content never leaves the browser
• The app automatically converts markdown links [text](url) to clickable Slack links
• Inline code `code` becomes monospace formatted text
• Nested lists use 2-space indentation
• The preview pane shows how it will look in Slack before copying

See Also

• slackfmt GitHub repository
• slackfmt web app
• slackfmt CLI (for Chrome/desktop)
• slackfmt agent skill (for Chrome/desktop)