Slack
OfficialSearch messages and files, send messages, manage canvases, and access user profiles.
Tools (13)
slack_send_message
Sends a message to a Slack channel or user. To DM a user, use their user_id as channel_id. If the user wants to send a message to themselves, the current logged in user's user_id is U08AX7WMX1S. Return the message link to the user. Message uses standard markdown (**bold**, _italic_, `code`, ~strikethrough~, lists, links, code blocks). Limited to 5000 chars per text element. Do not include sensitive info in link query params. Cannot post to externally shared (Slack Connect) channels. Thread replies: set thread_ts to parent message timestamp, reply_broadcast=true to also post to channel. Use slack_search_channels to find channel IDs, slack_search_users to find user IDs. If user has not reviewed the message, use slack_send_message_draft instead.
slack_schedule_message
Schedules a message for future delivery to a Slack channel. Does NOT send immediately — use slack_send_message for that. post_at must be a Unix timestamp at least 2 minutes in the future, max 120 days out. Message is markdown formatted. Once scheduled, cannot be edited via API — user should use "Drafts and sent" in Slack UI. Thread replies: provide thread_ts and optionally reply_broadcast=true. Cannot schedule in externally shared (Slack Connect) channels. Use slack_search_channels to find channel IDs, slack_search_users to find user IDs (usable as channel_id for DMs).
slack_create_canvas
Creates a Slack Canvas document from Canvas-flavored Markdown content. Return the canvas link to the user. Not available on free teams. Use slack_read_canvas to read existing canvases. Use slack_update_canvas to edit an existing canvas. ## Canvas Formatting Guidelines: REQUIRED: Must be a non-empty string when updating canvas content. Only omit this field if you are updating ONLY the title. The canvas content, formatted as Canvas-flavored Markdown. Canvas-flavored Markdown is different from Slack message formatting. When creating content for Canvases, adhere to the following Canvas-only rules: - The content should be formatted as standard Markdown, including headers, lists, links, checklists, and other Markdown formatting. - When writing user IDs, you should format them as: `` where `U15CTCJ83` is the user\'s Slack ID. - When user references are used in their own line, they will render as larger cards, if referenced inline they will render as special text. - When writing channel IDs, you should format them as: `` where `C15CTCJ83` is the channel\'s Slack ID. Always use the channel\'s ID, NEVER use the channel name. - NEVER output a channel as <#C1234567890> or a user as <@U1234567890>, even when part of a text quote, instead use the format above. - Links should be formatted as: `[link text](https://example.com)`. Do not surround the link in angle brackets. - IMPORTANT: Only use these URL schemes in links: `http://`, `https://`, `mailto:`, `tel:`, `ftp://`, `slack://`, or relative paths starting with `/`. Other schemes like `javascript:`, `data:`, `file:` will be automatically removed from the canvas. - Images should be formatted as: `` - Image syntax must appear only in a top-level, stand-alone line. Images are not supported in other elements - Salesforce records should be formatted as: `` where `<org_id>` is the Salesforce org ID and `<record_id>` is the Salesforce record ID, the org ID and record ID should be the full IDs which would be 18 characters long. Example: `` - Salesforce records syntax must appear only in a top-level, stand-alone line. Salesforce records are not supported in other elements - Quoted text should be formatted as: `> This is quoted text`, but you should only use quotes on their own line. - Slack-style emojis are supported, e.g. :tada: or :wave: - Use only ATX headings `#`, `##`, `###`. NEVER use deeper headings `####`-`######`. - Do not place headings inside list items. - In list items, allow only paragraphs with inline formatting. - Thematic breaks (---, ***, ___) are only allowed at the top level. - When nesting lists, do not mix list types: - Numbered lists can only contain nested numbered lists, and cannot contain nested bulleted lists - Bulleted lists can only contain nested bulleted lists, and cannot contain nested numbered lists - Code blocks are not allowed inside list items. - Tables should be formatted as, where <br> can be used for multi-line content: |Header|Header2| |---|---| |content1|content2<br>line two| - The title provided through the `title` field will be used as the title of the canvas. Do not include the title in the content section. <example1> # Headers # Status :large_green_circle: On Track # Goal The channel to coordinate the build, testing, and launch of Platypus # :people_hugging:Stakeholders   # :books:Resources * Project Plan * Google Drive # :slack:Related channels *  - Project Channel *  - [GTM Channel](https://gtm.wiki.com) </example1> <example2> |Message|User Author| |---|---| |[Here is the python guide](https://team.slack.com/archives/C016VCYCL74/p1727122965001469)|| |[The Java guide isn\'t ready](https://team.slack.com/archives/C016VCYCL74/p1727122965001469)||\n\n # Python Guide\n ## Step 1\n ```python print("Hello, world!") ```\n\n </example2> - When a layout is requested use the ::: {.layout} as the starting delimiter and ::: as the ending delimiter of the full layout. Then each column should be wrapped in ::: {.column} as the starting delimiter and ::: as the ending delimiter. There can only be up to 3 columns in a layout and tables and callouts are not supported in layouts or columns. - Callouts should be formatted with ::: {.callout} as the starting delimiter and ::: as the ending delimiter in markdown. Use them to highlight important information, such as warnings, important prerequisites, and notices. - Do not use tables within callouts and callouts cannot be nested within other elements. <example_markdown_with_callout> ::: {.callout} This is a callout ::: </example_markdown_with_callout> - In block quotes, ONLY use: plain text paragraphs with inline formatting. No headings, lists, code blocks, or nested quotes. - Code blocks are allowed only at the top level (not inside block quotes or list items). CRITICAL RESTRICTIONS - Canvas Nesting Rules (MUST FOLLOW): - In list items, ONLY use: plain text paragraphs with inline formatting (bold, italic, inline `code`, links). - Code blocks, block quotes, and headings must always be separated from lists by blank lines. - In layouts no tables or callouts are supported.- Layouts are not supported in tables or callouts. <example_correct_usage> - Item with inline `code` formatting - Item with **bold** text and [links](https://example.com) </example_correct_usage> <example_blocks_and_quotes_outside_lists> ``` code block at top level ``` - List item one - List item two > Block quote at top level ### Heading at top level </example_blocks_and_quotes_outside_lists> WHEN CITING SOURCES: - When your content references information from web search results or other sources, you MUST include inline citation links using the [[N]](url) format throughout the content, exactly as you would in a chat response. - Place citations inline next to the claims they support, e.g. "Shaidorov won gold [[7]](https://en.wikipedia.org/wiki/...)" - Do NOT collapse all sources into a single "Source:" line at the bottom. Each fact should be cited where it appears. - The citation links will be automatically enriched with page titles for readability. - Format date headings and key dates (including due dates, deadlines, milestones) as  ONLY. Never append day names or date text. ## Examples of appropriate usage of date formatting in your output: Correct usage: <example_date_heading_correct> ##  </example_date_heading_correct> Incorrect usage (has day name and date text): <example_date_heading_incorrect> ##  December 16th - Monday </example_date_heading_incorrect>- User Profile Cards: To display a user's profile card as a standalone section (not inline), use the format  where user_id is the Slack user ID. CRITICAL: Use parentheses () around @user_id, NOT angle brackets <>. Example: . Profile cards should be on their own line and will render as larger cards with user information. ## Examples of appropriate usage of user profile cards in your output: Correct usage (standalone profile card on its own line): <example_user_profile_card_correct> # Team Members   </example_user_profile_card_correct>- Slack Files: ONLY for files with URLs matching *.slack.com/files/*, ALWAYS embed using . For standalone display (card): place on its own line. For inline reference (clickable text): embed directly in paragraph like "The  contains...". Do not use this syntax for non-Slack files.
slack_update_canvas
Updates an existing Slack Canvas document with markdown content. Supports appending, prepending, or replacing content. ## CRITICAL WARNING Using `action=replace` WITHOUT providing a `section_id` will **OVERWRITE THE ENTIRE CANVAS** content. This is destructive and irreversible. You MUST call `slack_read_canvas` first to retrieve section IDs, then pass the appropriate `section_id` to replace only the target section. ## Action Behavior ### With `section_id`: - `append`: Adds new content to the END of the specified section's block (inserted after the last content under that section, just before the next header section) - `prepend`: Inserts new content immediately AFTER the targeted element. If the section_id is a header, content appears after the header line but before the section's existing body content. If the section_id is a non-header element (paragraph, list, table, etc.), content is inserted directly after that element. - `replace`: Replaces ONLY the specified section's content block (safe) **Important:** The `section_id_mapping` contains IDs for ALL content elements — headers (`#`, `##`, `###`), paragraphs, lists, tables, and callouts — not just header sections. For best results with append/prepend, target a header section_id to insert within that section's block. ### Without `section_id`: - `append`: Adds content to the END of the canvas (after the last section) - `prepend`: Inserts content after the canvas title but before existing body content (the title is preserved) - `replace`: ⚠️ **REPLACES THE ENTIRE CANVAS** — avoid unless user explicitly wants full replacement ## Args: canvas_id (str, required): ID of the canvas to update (e.g., "F1234567890") action (str, required): One of "append", "prepend", or "replace". Defaults to "append" content (str, required): Markdown-formatted content to insert or replace section_id (Optional[str]): Section ID from slack_read_canvas. Can reference any content element (header, paragraph, list, table, callout). For append/prepend, targeting a header section_id is recommended as it operates on the header's content block. append inserts after the last content in that section's block (before the next header); prepend inserts immediately after the targeted element; replace overwrites the section's block. STRONGLY RECOMMENDED for replace action to avoid overwriting the entire canvas. ## Returns: canvas_id (str): ID of the updated canvas canvas_url (str): URL link to the updated canvas — always share this with the user section_id_mapping (dict): Updated mapping of section IDs to their markdown content after the edit. Each key is a section ID string (e.g., "temp:C:abc123") and each value is the markdown content of that element. Contains IDs for ALL content elements (headers, paragraphs, lists, tables, callouts), not just headers. Use these section IDs in subsequent `slack_update_canvas` calls to target specific sections, enabling multi-step editing workflows without needing to call `slack_read_canvas` again between edits. ## When to Use - User wants to add content to an existing canvas (append/prepend) - User wants to update a specific section of a canvas (replace with section_id) - User wants to rewrite an entire canvas (replace without section_id — only if explicitly requested) ## When NOT to Use - User wants to create a new canvas (use `slack_create_canvas` instead) - User wants to read a canvas (use `slack_read_canvas` instead) - User only wants to send a simple message (use `slack_send_message` instead) ## Recommended Workflow for Editing a Section 1. Call `slack_read_canvas` with the canvas_id to get content and section IDs 2. Identify the target section_id from the section_id_mapping 3. Call `slack_update_canvas` with action=replace and the section_id ## Examples Append to the end of a canvas (no section_id): slack_update_canvas(canvas_id="F0123ABC456", action="append", content="## New Section Here is the appended content.") Append to the end of a specific section: slack_update_canvas(canvas_id="F0123ABC456", action="append", section_id="temp:C:abc123", content="## New Section This content is added at the end of the specified section.") Replace a specific section (safe — only that section is changed): slack_update_canvas(canvas_id="F0123ABC456", action="replace", section_id="temp:C:abc123", content="## Updated Section This replaces only the targeted section.") Prepend within a specific section (inserts right after the section header, before existing body content): slack_update_canvas(canvas_id="F0123ABC456", action="prepend", section_id="temp:C:abc123", content="This paragraph appears right after the section header, before the section's existing body content.") ## Error Codes: - `not_supported_free_team`: Canvas operations not supported on free teams - `canvas_not_found`: Invalid canvas_id or user lacks access - `invalid_content`: Content format is invalid - `permission_denied`: User lacks permission to edit this canvas - `section_not_found`: The provided section_id does not exist in the canvas ## Canvas Formatting Guidelines: REQUIRED: Must be a non-empty string when updating canvas content. Only omit this field if you are updating ONLY the title. The canvas content, formatted as Canvas-flavored Markdown. Canvas-flavored Markdown is different from Slack message formatting. When creating content for Canvases, adhere to the following Canvas-only rules: - The content should be formatted as standard Markdown, including headers, lists, links, checklists, and other Markdown formatting. - When writing user IDs, you should format them as: `` where `U15CTCJ83` is the user\'s Slack ID. - When user references are used in their own line, they will render as larger cards, if referenced inline they will render as special text. - When writing channel IDs, you should format them as: `` where `C15CTCJ83` is the channel\'s Slack ID. Always use the channel\'s ID, NEVER use the channel name. - NEVER output a channel as <#C1234567890> or a user as <@U1234567890>, even when part of a text quote, instead use the format above. - Links should be formatted as: `[link text](https://example.com)`. Do not surround the link in angle brackets. - IMPORTANT: Only use these URL schemes in links: `http://`, `https://`, `mailto:`, `tel:`, `ftp://`, `slack://`, or relative paths starting with `/`. Other schemes like `javascript:`, `data:`, `file:` will be automatically removed from the canvas. - Images should be formatted as: `` - Image syntax must appear only in a top-level, stand-alone line. Images are not supported in other elements - Salesforce records should be formatted as: `` where `<org_id>` is the Salesforce org ID and `<record_id>` is the Salesforce record ID, the org ID and record ID should be the full IDs which would be 18 characters long. Example: `` - Salesforce records syntax must appear only in a top-level, stand-alone line. Salesforce records are not supported in other elements - Quoted text should be formatted as: `> This is quoted text`, but you should only use quotes on their own line. - Slack-style emojis are supported, e.g. :tada: or :wave: - Use only ATX headings `#`, `##`, `###`. NEVER use deeper headings `####`-`######`. - Do not place headings inside list items. - In list items, allow only paragraphs with inline formatting. - Thematic breaks (---, ***, ___) are only allowed at the top level. - When nesting lists, do not mix list types: - Numbered lists can only contain nested numbered lists, and cannot contain nested bulleted lists - Bulleted lists can only contain nested bulleted lists, and cannot contain nested numbered lists - Code blocks are not allowed inside list items. - Tables should be formatted as, where <br> can be used for multi-line content: |Header|Header2| |---|---| |content1|content2<br>line two| - The title provided through the `title` field will be used as the title of the canvas. Do not include the title in the content section. <example1> # Headers # Status :large_green_circle: On Track # Goal The channel to coordinate the build, testing, and launch of Platypus # :people_hugging:Stakeholders   # :books:Resources * Project Plan * Google Drive # :slack:Related channels *  - Project Channel *  - [GTM Channel](https://gtm.wiki.com) </example1> <example2> |Message|User Author| |---|---| |[Here is the python guide](https://team.slack.com/archives/C016VCYCL74/p1727122965001469)|| |[The Java guide isn\'t ready](https://team.slack.com/archives/C016VCYCL74/p1727122965001469)||\n\n # Python Guide\n ## Step 1\n ```python print("Hello, world!") ```\n\n </example2> - When a layout is requested use the ::: {.layout} as the starting delimiter and ::: as the ending delimiter of the full layout. Then each column should be wrapped in ::: {.column} as the starting delimiter and ::: as the ending delimiter. There can only be up to 3 columns in a layout and tables and callouts are not supported in layouts or columns. - Callouts should be formatted with ::: {.callout} as the starting delimiter and ::: as the ending delimiter in markdown. Use them to highlight important information, such as warnings, important prerequisites, and notices. - Do not use tables within callouts and callouts cannot be nested within other elements. <example_markdown_with_callout> ::: {.callout} This is a callout ::: </example_markdown_with_callout> - In block quotes, ONLY use: plain text paragraphs with inline formatting. No headings, lists, code blocks, or nested quotes. - Code blocks are allowed only at the top level (not inside block quotes or list items). CRITICAL RESTRICTIONS - Canvas Nesting Rules (MUST FOLLOW): - In list items, ONLY use: plain text paragraphs with inline formatting (bold, italic, inline `code`, links). - Code blocks, block quotes, and headings must always be separated from lists by blank lines. - In layouts no tables or callouts are supported.- Layouts are not supported in tables or callouts. <example_correct_usage> - Item with inline `code` formatting - Item with **bold** text and [links](https://example.com) </example_correct_usage> <example_blocks_and_quotes_outside_lists> ``` code block at top level ``` - List item one - List item two > Block quote at top level ### Heading at top level </example_blocks_and_quotes_outside_lists> WHEN CITING SOURCES: - When your content references information from web search results or other sources, you MUST include inline citation links using the [[N]](url) format throughout the content, exactly as you would in a chat response. - Place citations inline next to the claims they support, e.g. "Shaidorov won gold [[7]](https://en.wikipedia.org/wiki/...)" - Do NOT collapse all sources into a single "Source:" line at the bottom. Each fact should be cited where it appears. - The citation links will be automatically enriched with page titles for readability. - Format date headings and key dates (including due dates, deadlines, milestones) as  ONLY. Never append day names or date text. ## Examples of appropriate usage of date formatting in your output: Correct usage: <example_date_heading_correct> ##  </example_date_heading_correct> Incorrect usage (has day name and date text): <example_date_heading_incorrect> ##  December 16th - Monday </example_date_heading_incorrect>- User Profile Cards: To display a user's profile card as a standalone section (not inline), use the format  where user_id is the Slack user ID. CRITICAL: Use parentheses () around @user_id, NOT angle brackets <>. Example: . Profile cards should be on their own line and will render as larger cards with user information. ## Examples of appropriate usage of user profile cards in your output: Correct usage (standalone profile card on its own line): <example_user_profile_card_correct> # Team Members   </example_user_profile_card_correct>- Slack Files: ONLY for files with URLs matching *.slack.com/files/*, ALWAYS embed using . For standalone display (card): place on its own line. For inline reference (clickable text): embed directly in paragraph like "The  contains...". Do not use this syntax for non-Slack files. ## What NOT to Expect: ❌ Does NOT create new canvases (use `slack_create_canvas`) ❌ Does NOT support setting canvas permissions or sharing ❌ Does NOT support deleting a canvas
slack_search_public
Searches for messages, files in public Slack channels ONLY. Current logged in user's user_id is U08AX7WMX1S. `slack_search_public` does NOT generally require user consent for use, whereas you should request and wait for user consent to use `slack_search_public_and_private`. --- `query` should include keywords or natural language question with search modifiers. Search modifiers: in:channel-name / in:<#C123456> / -in:channel Channel filter in:<@U123456> / in:@username DM filter from:<@U123456> / from:username Author filter (angle brackets are literal for IDs) to:<@U123456> / to:me Recipient filter creator:@user Canvas creator filter is:thread / is:saved / has:pin / has:link / has:file Content filters has::emoji: / hasmy::emoji: Reaction filters before:YYYY-MM-DD / after:YYYY-MM-DD / on:YYYY-MM-DD / during:month Date filters "exact phrase" / -word / * (wildcard, min 3 chars) Text matching File search: use `content_types="files"` with `type:` filter (images, documents, pdfs, spreadsheets, presentations, canvases, lists, emails, audio, videos). All standard modifiers work with file searches. Search types: 1. Natural language — Triggered by natural language questions. Finds topically related content even without exact keywords. May return broadly related results — combine with filters for precision. ✅ Semantic search is available for this user. 2. Keyword — exact matches, space-separated = AND, no boolean operators (AND/OR/NOT). Use slack_read_thread for thread details, slack_read_canvas for canvas content, slack_read_channel for surrounding messages. Strategy: break into multiple small searches, use modifiers to narrow, try keyword then semantic (or vice versa), broaden if 0 results. --- Examples: ✅ Use query="What's our holiday schedule? in:#general" query="bug report after:2024-01-08" sort="timestamp" query="from:<@Jane Doe> in:dev bug report" Additional parameters: include_context (Optional[bool]) Include surrounding context messages for each result (default: true). Set to false to reduce response size. max_context_length (Optional[int]) Max character length for each context message. Longer messages are truncated.
slack_search_public_and_private
Searches for messages, files in ALL Slack channels, including public channels, private channels, DMs, and group DMs. Current logged in user's user_id is U08AX7WMX1S. --- `query` should include keywords or natural language question with search modifiers. Search modifiers: in:channel-name / in:<#C123456> / -in:channel Channel filter in:<@U123456> / in:@username DM filter from:<@U123456> / from:username Author filter (angle brackets are literal for IDs) to:<@U123456> / to:me Recipient filter creator:@user Canvas creator filter is:thread / is:saved / has:pin / has:link / has:file Content filters has::emoji: / hasmy::emoji: Reaction filters before:YYYY-MM-DD / after:YYYY-MM-DD / on:YYYY-MM-DD / during:month Date filters "exact phrase" / -word / * (wildcard, min 3 chars) Text matching File search: use `content_types="files"` with `type:` filter (images, documents, pdfs, spreadsheets, presentations, canvases, lists, emails, audio, videos). All standard modifiers work with file searches. Search types: 1. Natural language — Triggered by natural language questions. Finds topically related content even without exact keywords. May return broadly related results — combine with filters for precision. ✅ Semantic search is available for this user. 2. Keyword — exact matches, space-separated = AND, no boolean operators (AND/OR/NOT). Use slack_read_thread for thread details, slack_read_canvas for canvas content, slack_read_channel for surrounding messages. Strategy: break into multiple small searches, use modifiers to narrow, try keyword then semantic (or vice versa), broaden if 0 results. --- Examples: ✅ Use (with user consent) query="What's our holiday schedule? in:#general" query="bug report after:2024-01-08" sort="timestamp" query="from:<@Jane Doe> in:dev bug report" Additional parameters: include_context (Optional[bool]) Include surrounding context messages for each result (default: true). Set to false to reduce response size. max_context_length (Optional[int]) Max character length for each context message. Longer messages are truncated.
slack_search_channels
Search for Slack channels by name or description. Returns channel names, IDs, topics, purposes, and archive status. Query tips: use terms matching channel names/descriptions (e.g., "engineering", "project alpha"). Names are typically lowercase with hyphens. Use slack_read_channel to read messages from a known channel. Use slack_search_public to search message content across channels.
slack_search_users
Search for Slack users by name, email, or profile attributes (department, role, title). Current logged in user's Slack user_id is U08AX7WMX1S. Query syntax: full names ("John Smith"), partial names ("John"), emails ("john@company.com"), departments/roles ("engineering"), combinations ("John engineering"), exclusions ("engineering -intern"). Space-separated terms = AND. Use slack_read_user_profile for detailed info on a known user ID. Use slack_search_public with from: filter to find messages by a user.
slack_read_channel
Reads messages from a Slack channel in reverse chronological order (newest first). To read DM history, use a user_id as channel_id. Read-only. Use slack_read_thread with message_ts to read thread replies. Use slack_search_channels to find a channel ID by name. Use slack_search_public to search across channels. If 'channel_not_found', try slack_search_channels first.
slack_read_thread
Reads messages from a specific Slack thread (parent message + all replies). Read-only. Requires channel_id and message_ts of the parent message. Use slack_search_public or slack_read_channel to find these values. Use slack_search_public with "is:thread" to find threads by content. Use slack_send_message with thread_ts to reply to a thread.
slack_read_canvas
Retrieves the markdown content and section ID mapping of a Slack Canvas document. Read-only. Use slack_create_canvas to create new canvases. Use slack_search_public to find canvases by name or content. Use slack_update_canvas to edit canvas content.
slack_read_user_profile
Retrieves detailed profile information for a Slack user: contact info, status, timezone, organization, and role. Read-only. Defaults to current user if user_id not provided. Use slack_search_users to find a user ID by name or email.
slack_send_message_draft
Creates a draft message in a Slack channel. The draft is saved to the user's "Drafts & Sent" in Slack without sending it. ## When to Use - User wants to prepare a message without sending it immediately - User needs to compose a message for later review or sending - User wants to draft a message to a specific channel ## When NOT to Use - User wants to send a message immediately (use `slack_send_message` instead) - User wants to schedule a message (use `slack_send_message` with scheduling) - User wants to create drafts in multiple channels (call this tool multiple times) - Channel is externally shared (Slack Connect channel) - drafts in externally shared channels are not supported ## Input Parameters: - `channel_id`: Single channel ID where the draft should be created - `message`: The draft message content using standard markdown. Supports **bold**, _italic_, `code`, ~strikethrough~, >blockquotes, lists, links, and code blocks. - `thread_ts` (optional): Timestamp of the parent message to create a draft reply in a thread (e.g., "1234567890.123456") ## Output: Returns `channel_link` - a Slack web client URL (e.g., https://app.slack.com/client/T123/C456) that opens the channel in the web app where the draft was created. ## Finding value for `channel_id` input: - Use `slack_search_users` tool to find user ID for DMs, then use their user_id as the channel_id ## Error Codes: - `channel_not_found`: Invalid channel ID or user does not have access to the channel - `draft_already_exists`: A draft already exists for this channel (user should edit or delete the existing draft first) - `failed_to_create_draft`: Draft creation failed for an unknown reason - `mcp_externally_shared_channel_restricted`: Cannot create drafts in externally shared channels (Slack Connect channels) ## Notes: - Drafts are created as attached drafts (linked to the specific channel) - User must have write access to the channel - Only one attached draft is allowed per channel - if a draft already exists, you'll get an error