slack-messaging
Use when writing, drafting, scheduling, or improving a Slack message, announcement, or reply sent via the Slack MCP tools (slacksendmessage, slacksendmessagedraft, slackschedulemessage). Covers Slack markdown formatting, message structure, thread etiquette, reactions, and scheduling, and points to the right dialect for canvases and Block Kit.
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Install
Works with every agent the skills CLI supports.
npx skills add https://github.com/slackapi/slack-skills-plugin --skill slack-messaging- 01
Install
Run the command in your project. The CLI asks which agents to install for.
- 02
Describe the task
Ask your agent for something this skill covers. It loads slack-messaging automatically when relevant.
- 03
Review the result
The agent follows the SKILL.md steps, scripts and references bundled with the skill.
SKILL.md
The instructions your agent reads when the skill is triggered.
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.
| Format | Syntax |
|---|---|
| Bold | **text** |
| Italic | _text_ (or *text*) |
| Strikethrough | ~~text~~ |
| Code (inline) | `code` |
| Quote | > text |
| Link | [display text](url) |
| Bulleted list | - item |
| Numbered list | 1. item |
Block elements also work. Write them as literal markdown:
-
Code block with an optional language for syntax highlighting:
```python print("hello") ``` -
Table with
|delimiters (escape a literal pipe inside a cell as\|):| Feature | Status | |---------|--------| | Tables | works | -
Headers with
#/##/###:## Section title
The one thing that does not embed in a message: inline images () 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:
#generalis usually more formal than#random. - For simple acknowledgments, add an emoji reaction with
slack_add_reactioninstead of a reply message (useslack_get_reactionsto read existing reactions). - When writing announcements, use a clear structure: context, key info, call to action.
Scheduling
- Use
slack_schedule_messageto post later.post_atis 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_canvasuses Canvas-flavored Markdown, a richer dialect than the message tools: headers, tables, checklists, and inline images () all embed, and it also supports user/channel reference cards, callouts, and columns. Do not assume the message rules above apply — follow theslack_create_canvastool'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
slack:block-kitskill, which composes and validates the block payload. For calling the Slack Web API directly (chat.postMessageand friends) rather than the MCP tools, use theslack:slack-apiskill.
FAQ
What does the slack-messaging skill do?
Use when writing, drafting, scheduling, or improving a Slack message, announcement, or reply sent via the Slack MCP tools (slacksendmessage, slacksendmessagedraft, slackschedulemessage). Covers Slack markdown formatting, message structure, thread etiquette, reactions, and scheduling, and points to the right dialect for canvases and Block Kit.
How do I install slack-messaging?
Run npx skills add https://github.com/slackapi/slack-skills-plugin --skill slack-messaging in your project. The skills CLI detects the agents you use and copies the skill into the right folder. For Claude Code you can also place the skill folder at ~/.claude/skills/slack-messaging/ (personal) or .claude/skills/slack-messaging/ (project).
Which AI agents can use slack-messaging?
Any agent that supports the open Agent Skills format (a folder with a SKILL.md file), including Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, Windsurf, Cline, OpenCode and more.
Is slack-messaging safe to install?
No partner security audit is available yet. Skills can run commands and scripts, so read the SKILL.md and any bundled files before installing.
Who maintains slack-messaging?
It is published by slackapi in slackapi/slack-skills-plugin. It has 2,948 recorded installs.
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