Slack Messaging Best Practices

This skill provides guidance for composing well-formatted, effective Slack messages.

When to Use

Apply this skill whenever composing, drafting, or helping the user write a Slack message — including when using slack_send_message, slack_send_message_draft, or slack_create_canvas.

Slack Formatting (mrkdwn)

Slack uses its own markup syntax called mrkdwn, which differs from standard Markdown. Always use mrkdwn when composing Slack messages:

Format	Syntax	Notes
Bold	*text*	Single asterisks, NOT double
Italic	_text_	Underscores
Strikethrough	~text~	Tildes
Code (inline)	`code`	Backticks
Code block	```code```	Triple backticks
Quote	> text	Angle bracket
Link	<url|display text>	Pipe-separated in angle brackets
User mention	<@U123456>	User ID in angle brackets
Channel mention	<#C123456>	Channel ID in angle brackets
Bulleted list	- item or • item	Dash or bullet character
Numbered list	1. item	Number followed by period

Common Mistakes to Avoid

• Do NOT use **bold** (double asterisks) — Slack uses *bold* (single asterisks)
• Do NOT use ## headers — Slack does not support Markdown headers. Use *bold text* on its own line instead.
• Do NOT use [text](url) for links — Slack uses <url|text> format
• Do NOT use --- for horizontal rules — Slack does not render these

Message Structure Guidelines

• Lead with the point. Put the most important information in the first line. Many people read Slack on mobile or in notifications where only the first line shows.
• Keep it short. Aim for 1-3 short paragraphs. If the message is long, consider using a Canvas instead.
• Use line breaks generously. Walls of text are hard to read. Separate distinct thoughts with blank lines.
• Use bullet points for lists. Anything with 3+ items should be a list, not a run-on sentence.
• Bold key information. Use *bold* for names, dates, deadlines, and action items so they stand out when scanning.

Thread vs. Channel Etiquette

• Reply in threads when responding to a specific message to keep the main channel clean.
• Use reply_broadcast (also post to channel) only when the reply contains information everyone needs to see.
• Post in the channel (not a thread) when starting a new topic, making an announcement, or asking a question to the whole group.
• Don't start a new thread to continue an existing conversation — find and reply to the original message.

Tone and Audience

• Match the tone to the channel — #general is usually more formal than #random.
• Use emoji reactions instead of reply messages for simple acknowledgments (though note: the MCP tools can't add reactions, so suggest the user do this manually if appropriate).
• When writing announcements, use a clear structure: context, key info, call to action.