slack-post — write a message to Slack with the right identity

Posting to Slack happens under one of two identities, and the choice is not cosmetic — it changes who the workspace sees as the author, what the message can @-mention, and which audit trail it lands in. This skill makes that choice explicit and consistent.

The two identities

The plugin runs two Slack MCP servers, each pinned to one identity:

Identity	Server	Tool	Posts as	When
User (default)	slack	mcp__plugin_adk_slack__conversations_add_message	you (your xoxp user token)	default — every post unless the prompt asks for the bot
Bot	slack-bot	mcp__plugin_adk_slack-bot__conversations_add_message	the Slack app/bot (xoxb token)	only when the prompt explicitly asks

Why two servers: the underlying slack-mcp-server cannot switch identity per call — with both tokens present it always prefers the user token. So the bot identity lives in its own server (slack-bot, launched with the bot token only, exposing just the post tool).

Decision: which identity?

Default to the user. Post via slack unless the prompt clearly opts into the bot. Signals that mean use the bot:

• "post as the bot / as the app / using the bot"
• "use the bot to send this"
• an explicit --as bot

Anything else — including silence — means post as you. Do not ask which identity to use; the default is user. (If the prompt is genuinely ambiguous — e.g. "have the bot or me post, whichever" — then, and only then, ask with AskUserQuestion.)

When you post as the bot, the bot must already be a member of the target channel, or Slack rejects the post (not_in_channel). If that happens, say so and suggest inviting the app — don't silently fall back to the user identity.

Always: the footer

Every message this skill sends — user or bot — ends with the footer:

_Sent using Claude_

Append it as the final line, separated by a blank line:

<the message body>

_Sent using Claude_

This is non-negotiable and applies to both identities. (To change the footer text, edit the line above — it is the single source of truth.)

Steps

1. Resolve the target. Turn --to / "#channel" / "@user" into a channel or user ID if needed (channels_list, users_search on the slack server). A thread reply needs the parent thread_ts.
2. Pick the identity per the decision rule above. Default user; bot only on explicit request.
3. Compose the body, then append the Sent using Claude footer as the final line.
4. Post via the matching tool:
   • user → mcp__plugin_adk_slack__conversations_add_message
   • bot → mcp__plugin_adk_slack-bot__conversations_add_message
5. Confirm back to the human: which channel, which identity, and a link/ts if returned. If Slack rejected the post (e.g. not_in_channel, channel_not_found), report the raw error and the fix — never retry under a different identity to "make it work".

Rules

• Posting is outward-facing. Show the human the exact message text and the resolved target+identity, and post only on a clear instruction to send. If they're still drafting, draft — don't send.
• Never escalate identity to dodge an error. A bot not_in_channel failure is reported, not worked around by quietly posting as the user (that changes the author the recipient sees).
• No mass posting. This skill sends the message the human asked for, to the target(s) they named — not a fan-out across channels.
• Reads don't belong here. Searching, fetching history, or listing members is the slack server's read tools directly — no skill, no footer, no identity decision.