slack-message-formatter

Slack Message Formatter

A Claude Code skill that formats messages for Slack with pixel-perfect accuracy. Converts standard Markdown to Slack-compatible output with two delivery paths:

1. Copy-paste — Rich HTML that preserves formatting when pasted into Slack's compose box
2. API/Webhook — Slack mrkdwn syntax for bots, automation, and CI/CD

Why?

• Slack uses mrkdwn (not Markdown). **bold** doesn't work — you need *bold*.
• Existing tools handle conversion well, but none combine generation + preview + copy-paste in one workflow.
• Programmatic clipboard doesn't preserve tables in Slack. Manual browser copy does.
• This skill gives you both paths: copy-paste for humans, webhook for bots.

Zero dependencies. 172+ tests. Built for Claude Code.

Install

Claude Code (recommended)

claude plugin marketplace add karanb192/slack-message-formatter
claude plugin install slack-message-formatter@slack-message-formatter

Codex

curl -sSL https://raw.githubusercontent.com/karanb192/slack-message-formatter/main/install.sh | bash -s codex

Manual install (curl)

# Claude Code global
curl -sSL https://raw.githubusercontent.com/karanb192/slack-message-formatter/main/install.sh | bash

# Codex global
curl -sSL https://raw.githubusercontent.com/karanb192/slack-message-formatter/main/install.sh | bash -s codex

# Current project only (auto-detects Claude Code or Codex)
curl -sSL https://raw.githubusercontent.com/karanb192/slack-message-formatter/main/install.sh | bash -s project

Updating

The marketplace tracks the main branch of this repo. Claude Code auto-updates marketplace plugins at startup, so most users will pick up changes on their next restart.

To refresh immediately without restarting:

/plugin marketplace update slack-message-formatter
/reload-plugins

Uninstall

# Claude Code
rm -rf ~/.claude/skills/slack-message-formatter

# Codex
rm -rf "${CODEX_HOME:-$HOME/.codex}/skills/slack-message-formatter"

Then in Claude Code, just ask:

• "Write a Slack message announcing our v2.5 release"
• "Format this for Slack"
• /slack-message-formatter

Standalone CLI

echo '**bold** and *italic*' | node src/run.mjs html
# → <b>bold</b> and <i>italic</i>

echo '**bold** and *italic*' | node src/run.mjs mrkdwn
# → *bold* and _italic_

echo '## Announcement' | node src/run.mjs preview
# → Opens browser with Slack-themed preview + copy page

Features

Copy-Paste Path (Rich HTML)

• Opens a clean HTML page in your browser
• Cmd+A, Cmd+C, then Cmd+V in Slack
• Preserves: bold, italic, strikethrough, links, lists, nested lists, code blocks, blockquotes, headings, task lists, tables (as code blocks), horizontal rules

API/Webhook Path (mrkdwn)

• Converts to Slack's native mrkdwn format
• Send directly via webhook:

  echo '**hello**' | node src/run.mjs send
  

• Requires CCH_SLA_WEBHOOK environment variable

Conversion Reference

Markdown	Slack mrkdwn	HTML (paste)
**bold**	*bold*	<b>bold</b>
*italic*	_italic_	<i>italic</i>
~~strike~~	~strike~	<s>strike</s>
`code`	`code`	<code>code</code>
[text](url)	<url|text>	<a href="url">text</a>
# Heading	*Heading*	<b>Heading</b>
- [x] Done	:white_check_mark: Done	✅ Done
- [ ] Todo	:black_square_button: Todo	⬜ Todo
Tables	Code block	Code block
---	━━━━━━━━━━	<hr>
:tada:	:tada: (Slack renders)	🎉 (Unicode)

Commands

Command	What it does
preview	Opens browser with copy page + dark preview
send	Sends via Slack webhook (mrkdwn)
html	Outputs raw HTML to stdout
mrkdwn	Outputs raw mrkdwn to stdout

Configuration

Env Variable	Default	Description
SLACK_FORMATTER_PREVIEW_DIR	/tmp/slack-formatter	Directory for preview HTML files
CCH_SLA_WEBHOOK	(none)	Slack webhook URL for send command

How It Works

Markdown → Parser → Dual Renderer
                    ├── Rich HTML → Browser → Cmd+C → Slack paste
                    └── mrkdwn   → Webhook → Slack API

1. You write Markdown (or Claude generates it)
2. The converter transforms it deterministically — same input always produces same output
3. Two outputs: Rich HTML for copy-paste, mrkdwn for API

Tables are rendered as aligned code blocks because Slack's paste handler breaks HTML <table> tags when mixed with other rich content.

Key Discovery: Slack Paste Limitations

Through extensive testing, we discovered: