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UpdatedJune 24, 2026 at 09:09

How to use the Slack connector's tools — sending and scheduling messages, replying in threads, reading channel history, searching the workspace, adding reactions, and resolving channels and users. Use when the user works with Slack, channels, DMs, threads, messages, reactions, or wants to post or look something up in a workspace.

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NimbleBrainInc

NimbleBrainInc/connector-skills

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SKILL.md

readonly

name	slack
description	How to use the Slack connector's tools — sending and scheduling messages, replying in threads, reading channel history, searching the workspace, adding reactions, and resolving channels and users. Use when the user works with Slack, channels, DMs, threads, messages, reactions, or wants to post or look something up in a workspace.

You are using the Slack connector (via Composio). Its tools act on the connected workspace as the authorized user/bot. Apply this guidance whenever you touch Slack.

Resolve the target first — use IDs, not names

Most tools take a channel. Prefer a channel ID (C… public, G… private, D… DM) over a #name. Name resolution is unreliable and fails outright on org-wide tokens. Resolve a human reference with the find-channels tool (SLACK_FIND_CHANNELS, by query) or list-channels before posting.
To DM or @-mention a person, resolve them to a user ID first — find-user-by-email (SLACK_FIND_USER_BY_EMAIL_ADDRESS) or list-users. Mention in text as <@U012ABC>, not @name.

Posting and replying

Send (SLACK_SEND_MESSAGE) requires channel and at least one content field (text, markdown_text, blocks, or attachments) — omitting all errors with no_text. Keep a message body under ~4000 chars; split or thread longer content.
A reply must pass thread_ts = the parent message's ts (the original, never a reply's ts). Timestamps are strings with fractional precision ("1700000000.123456"); pass them exactly as returned.
Slack uses mrkdwn, not full Markdown: *bold*, _italic_, ~strike~, > quote, `code`. Links are <url|label>. There are no # headings.
Edit with the update-message tool and delete with the delete tool — both need the exact ts + channel. To react, add-reaction (SLACK_ADD_REACTION_TO_AN_ITEM) takes the emoji name (no colons), channel, and message timestamp.

Reading and searching

Channel history (SLACK_FETCH_CONVERSATION_HISTORY) returns the main timeline only — threaded replies are not included. To read a thread, call fetch-message-thread with the channel and the parent ts. Page with cursor; bound with oldest/latest rather than pulling everything.
Search (SLACK_SEARCH_MESSAGES) is workspace-wide and uses Slack search operators, not plain keywords: in:#channel, from:@user, before:YYYY-MM-DD, after:YYYY-MM-DD, has:link, has::emoji:. Combine them (deploy in:#eng from:@alice after:2026-01-01) instead of fetching broad and filtering yourself. Search only sees content the connected identity can access.

Care

Posting is immediate and visible to everyone in the channel — there is no draft state. Confirm the channel (right C… id, public vs. private) and the content before sending, especially for @here/@channel or cross-channel posts.
Delete is irreversible, and only the original author/bot can delete its own messages. Never bulk-delete or bulk-react without explicit scope.
Don't @-mention broadly (@channel, @here) unless asked — it notifies everyone. Scheduled messages (SLACK_SCHEDULE_MESSAGE, post_at = future Unix time) still fire later; say so when you set one.
Honor rate limits (~1 message/sec; HTTP 429 carries Retry-After). When in doubt about which channel, ask rather than guessing — a wrong-channel post is user-visible and hard to undo cleanly.

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name	slack
description	How to use the Slack connector's tools — sending and scheduling messages, replying in threads, reading channel history, searching the workspace, adding reactions, and resolving channels and users. Use when the user works with Slack, channels, DMs, threads, messages, reactions, or wants to post or look something up in a workspace.

You are using the Slack connector (via Composio). Its tools act on the connected workspace as the authorized user/bot. Apply this guidance whenever you touch Slack.

Resolve the target first — use IDs, not names

Most tools take a channel. Prefer a channel ID (C… public, G… private, D… DM) over a #name. Name resolution is unreliable and fails outright on org-wide tokens. Resolve a human reference with the find-channels tool (SLACK_FIND_CHANNELS, by query) or list-channels before posting.
To DM or @-mention a person, resolve them to a user ID first — find-user-by-email (SLACK_FIND_USER_BY_EMAIL_ADDRESS) or list-users. Mention in text as <@U012ABC>, not @name.

Posting and replying

Send (SLACK_SEND_MESSAGE) requires channel and at least one content field (text, markdown_text, blocks, or attachments) — omitting all errors with no_text. Keep a message body under ~4000 chars; split or thread longer content.
A reply must pass thread_ts = the parent message's ts (the original, never a reply's ts). Timestamps are strings with fractional precision ("1700000000.123456"); pass them exactly as returned.
Slack uses mrkdwn, not full Markdown: *bold*, _italic_, ~strike~, > quote, `code`. Links are <url|label>. There are no # headings.
Edit with the update-message tool and delete with the delete tool — both need the exact ts + channel. To react, add-reaction (SLACK_ADD_REACTION_TO_AN_ITEM) takes the emoji name (no colons), channel, and message timestamp.

Reading and searching

Channel history (SLACK_FETCH_CONVERSATION_HISTORY) returns the main timeline only — threaded replies are not included. To read a thread, call fetch-message-thread with the channel and the parent ts. Page with cursor; bound with oldest/latest rather than pulling everything.
Search (SLACK_SEARCH_MESSAGES) is workspace-wide and uses Slack search operators, not plain keywords: in:#channel, from:@user, before:YYYY-MM-DD, after:YYYY-MM-DD, has:link, has::emoji:. Combine them (deploy in:#eng from:@alice after:2026-01-01) instead of fetching broad and filtering yourself. Search only sees content the connected identity can access.

Care

Posting is immediate and visible to everyone in the channel — there is no draft state. Confirm the channel (right C… id, public vs. private) and the content before sending, especially for @here/@channel or cross-channel posts.
Delete is irreversible, and only the original author/bot can delete its own messages. Never bulk-delete or bulk-react without explicit scope.
Don't @-mention broadly (@channel, @here) unless asked — it notifies everyone. Scheduled messages (SLACK_SCHEDULE_MESSAGE, post_at = future Unix time) still fire later; say so when you set one.
Honor rate limits (~1 message/sec; HTTP 429 carries Retry-After). When in doubt about which channel, ask rather than guessing — a wrong-channel post is user-visible and hard to undo cleanly.