Slack Messaging Skill for Claude

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 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.