slack-messaging

anthropics/knowledge-work-plugins

Guidance for composing well-formatted, effective Slack messages using mrkdwn syntax

What is slack-messaging?

This skill provides best practices for writing Slack messages with proper mrkdwn formatting, structure, and etiquette. Use it whenever composing, drafting, or helping write Slack messages to ensure they are clear, well-formatted, and appropriate for your audience.

Format text with mrkdwn syntax (bold, italic, code, links, mentions, lists)
Structure messages for clarity with line breaks, bullet points, and key information highlighted
Apply thread vs. channel etiquette to keep conversations organized
Match tone and style to different Slack channels and contexts
Avoid common formatting mistakes that break Slack message appearance

How to install slack-messaging

npx skills add https://github.com/anthropics/knowledge-work-plugins --skill slack-messaging

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How to use slack-messaging

1.Review the mrkdwn syntax table to understand Slack's formatting rules (single asterisks for bold, underscores for italic, angle brackets for links)
2.Structure your message by leading with the most important information on the first line
3.Use line breaks and bullet points to separate ideas and keep text scannable
4.Bold key information like names, dates, deadlines, and action items using *text* syntax
5.Decide whether to post in the channel or reply in a thread based on whether the message starts a new topic or responds to an existing one

Use cases

Good for

Drafting announcements or important updates for team channels
Composing professional messages with proper formatting and emphasis
Organizing information with lists and code blocks in Slack
Deciding whether to reply in a thread or post to the main channel
Writing clear action items and deadlines that stand out to readers

Who it's for

Anyone composing Slack messages
Team leads writing announcements
Developers sharing code snippets or technical updates
Project managers communicating deadlines and action items

slack-messaging FAQ

Why does my bold text not work in Slack?

Slack uses single asterisks for bold (*text*), not double asterisks (**text**). Double asterisks will not render as bold in Slack.

How do I create a link in Slack?

Use the format <url|display text> with the URL and display text separated by a pipe character inside angle brackets. Standard Markdown link syntax [text](url) does not work in Slack.

Can I use headers in Slack messages?

No, Slack does not support Markdown headers like ## or ###. Instead, use bold text on its own line (*bold text*) to create visual separation and emphasis.

When should I reply in a thread vs. post to the channel?

Reply in threads when responding to a specific message to keep the channel clean. Post directly to the channel when starting a new topic, making an announcement, or asking a question to the whole group.

What should I do if my message is getting too long?

Aim for 1-3 short paragraphs. If your message is longer, consider using a Slack Canvas instead, which is better suited for detailed or lengthy content.

Full instructions (SKILL.md)

Source of truth, from anthropics/knowledge-work-plugins.

name: slack-messaging description: Guidance for composing well-formatted, effective Slack messages using mrkdwn syntax

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.