slackapi/slack-mcp-plugin/slack-messaging

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_schedule_message. The formatting rules below cover these message tools. slack_create_canvas uses a different, richer markdown dialect — see the Canvas note below.

Formatting

The message tools (slack_send_message, slack_send_message_draft, slack_schedule_message) accept standard markdown and convert it to Slack formatting on send. Write normal markdown. Do not use Slack's legacy mrkdwn syntax (*bold*, ~strike~); those single-character forms mean something different in standard markdown. Each text element is limited to ~5000 characters.

Block elements also work. Write them as literal markdown:

• Code block with an optional language for syntax highlighting:

```text `python print("hello") ` ```

• Table with | delimiters (escape a literal pipe inside a cell as \|):

```text

```

• Headers with # / ## / ###:

``text ## Section title ``

The one thing that does not embed in a message: inline images (![alt](url)) typically render as a plain link rather than an inline image. For rich embedded layouts (buttons, images, structured cards) you need Block Kit; for a document-style surface where images do embed, use a canvas. See the Notes below.

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 (the ~5000-character limit is a ceiling, not a target). If the message is long or structured, consider 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.
• For simple acknowledgments, add an emoji reaction with slack_add_reaction instead of a reply message (use slack_get_reactions to read existing reactions).
• When writing announcements, use a clear structure: context, key info, call to action.

Scheduling

• Use slack_schedule_message to post later. post_at is a Unix timestamp that must be at least 2 minutes in the future and at most 120 days out; the message body uses the same standard markdown as above.
• Scheduled messages can't be edited via the API once set — the user manages them from Drafts & sent in Slack.

Notes

• Canvas formatting is different. slack_create_canvas uses Canvas-flavored Markdown, a richer dialect than the message tools: headers, tables, checklists, and inline images (![alt](url)) all embed, and it also supports user/channel reference cards, callouts, and columns. Do not assume the message rules above apply — follow the slack_create_canvas tool's own formatting guidance when composing a canvas.
• Scope: this skill owns composing and formatting the _text_ of messages sent through the Slack MCP message tools. For interactive layouts (buttons, menus, modals, Home tabs, or any Block Kit JSON), use the block-kit skill, which composes and validates the block payload. For calling the Slack Web API directly (chat.postMessage and friends) rather than the MCP tools, use the slack-api skill.