post-to-slack

name	post-to-slack
description	Post a message to a Slack channel, resolving channel/user names to IDs and adding an optional @mention or thread reply. Use when the user wants to post, share, or notify something in Slack, or when another skill needs to deliver its output to a Slack channel.
disable-model-invocation	true

Post to Slack

Resolves a channel name (or a user name for a mention) to its Slack ID before posting — the Slack MCP connector's send/search tools need IDs, not display names, and IDs are not stable across workspaces.

Steps

1. Determine the message body and the target channel. If the caller (a direct user request, or another skill such as report-pbl-progress) already gives an explicit channel ID (C...) and/or an already-resolved mention (<@U...>), skip straight to step 4 — don't re-resolve what's already unambiguous.
2. If the channel is given by name rather than ID, resolve it with the Slack MCP connector's slack_search_channels tool and take the matching channel's ID. If more than one channel plausibly matches, ask the user rather than guessing.
3. If a mention is wanted and given by name rather than user ID, resolve it with slack_search_users and format it as <@USERID> inline in the message text — Slack does not render @name as a mention, only the raw <@ID> form works.
4. Post with slack_send_message (thread_ts for a thread reply, reply_broadcast to also surface a thread reply in the channel). Return the message's permalink to the caller.

Reference

Failure modes

• Channel not found: slack_search_channels found no match — confirm the exact channel name with the user; don't guess a close match.
• User not found: same for slack_search_users when resolving a mention.
• Message too long: 5000 characters per text element — split into a thread reply rather than truncating silently.
• Can't post to Slack Connect (externally shared) channels: slack_send_message fails outright for these; tell the user rather than retrying.
• Slack Canvas unavailable: slack_create_canvas returns not_supported_free_team on free-tier workspaces. This skill never uses Canvas for that reason — if a caller wants a richer document than a single message, that's out of this skill's scope.

Reusable from other skills

This skill is intentionally generic — it has no PBL/monday-specific logic. Any skill that produces a summary a human should see in Slack (e.g. report-pbl-progress) should hand this skill the message text and target channel rather than calling the Slack MCP tools directly itself. This also keeps unattended/scheduled callers working: a caller that already knows its channel and mention can drive this skill's steps straight through without any ambiguity to resolve.