slack

name	slack
description	Read, send, and manage Slack messages via the Web API
compatibility	Designed for Vellum personal assistants
metadata	{"icon":"assets/icon.svg","emoji":"💬","vellum":{"category":"messaging","display-name":"Slack"}}

You help users interact with their Slack workspace. All Slack operations use the Slack Web API directly via assistant oauth request --provider slack_channel -- there are no dedicated Slack tools. Use relative Slack API method paths such as /chat.postMessage; the provider supplies the Slack host.

Resolution Scripts

Use these scripts to resolve Slack channel and user names to IDs. Results are cached locally so repeated lookups are free (no API calls).

Command	Description
bun skills/slack/scripts/slack-resolve.ts channel <name>	Resolve a channel name to its ID
bun skills/slack/scripts/slack-resolve.ts user <name-or-email>	Resolve a user display name or email to their ID
bun skills/slack/scripts/slack-resolve.ts channels [--refresh]	List all cached channels, or refresh the cache

All scripts return JSON:

• Success: { "ok": true, "data": { "id": "C...", "name": "general", ... } }
• Failure: { "ok": false, "error": "..." }

The cache is stored locally under $VELLUM_WORKSPACE_DIR/data/slack-skill/. On first use the script fetches all channels/users from Slack and caches them. Subsequent lookups read from the cache with no API calls. Pass --refresh to force a refresh.

Making Slack API Calls

Use assistant oauth request --provider slack_channel to call any Slack Web API method. Auth is handled transparently -- the provider injects the bot token automatically. Pass relative method paths; do not include a host.

General pattern:

assistant oauth request --provider slack_channel \
  -X POST \
  -d '{"channel":"C123","text":"Hello world"}' \
  /chat.postMessage --json

The model knows the full Slack API from training data. Refer to https://api.slack.com/methods for the complete list of available endpoints.

Send a message

assistant oauth request --provider slack_channel \
  -X POST \
  -d '{"channel":"C0123456789","text":"Hello from the assistant!"}' \
  /chat.postMessage --json

Read channel history

assistant oauth request --provider slack_channel \
  -X POST \
  -d '{"channel":"C0123456789","limit":20}' \
  /conversations.history --json

Read thread replies

assistant oauth request --provider slack_channel \
  -X POST \
  -d '{"channel":"C0123456789","ts":"1716000000.000001"}' \
  /conversations.replies --json

Add a reaction

assistant oauth request --provider slack_channel \
  -X POST \
  -d '{"channel":"C0123456789","timestamp":"1716000000.000001","name":"thumbsup"}' \
  /reactions.add --json

Send with blocks (rich formatting)

assistant oauth request --provider slack_channel \
  -X POST \
  -d '{
    "channel":"C0123456789",
    "text":"Fallback text",
    "blocks":[
      {"type":"header","text":{"type":"plain_text","text":"Weekly Update"}},
      {"type":"section","text":{"type":"mrkdwn","text":"*Project Alpha*: on track\n*Project Beta*: needs review"}}
    ]
  }' \
  /chat.postMessage --json

Upload a file

File uploads use a multi-step flow: get an upload URL, upload the file, then complete the upload.

# Step 1: Get an upload URL
assistant oauth request --provider slack_channel \
  -X POST \
  -d '{"filename":"notes.txt","length":42}' \
  /files.getUploadURLExternal --json

# Step 2: Upload file content to the returned upload_url (use curl directly)
# Step 3: Complete the upload
assistant oauth request --provider slack_channel \
  -X POST \
  -d '{"files":[{"id":"FILE_ID","title":"Meeting Notes"}],"channel_id":"C0123456789"}' \
  /files.completeUploadExternal --json

Search messages

assistant oauth request --provider slack_channel \
  "/search.messages?query=project+launch+in%3A%23general" --json

Open a DM

assistant oauth request --provider slack_channel \
  -X POST \
  -d '{"users":"U0123456789"}' \
  /conversations.open --json

Typical Workflow

1. Resolve the channel: bun skills/slack/scripts/slack-resolve.ts channel general to get the channel ID.
2. Call the API: Use assistant oauth request --provider slack_channel with that ID for the actual operation (send, read, react, etc.).
3. For DMs: Use bun skills/slack/scripts/slack-resolve.ts user <name> to get the user ID, then conversations.open to get the DM channel ID, then chat.postMessage to send the message.

User Resolution

When you need to send a DM or look up a Slack user by name, check contacts first to avoid redundant API calls:

1. Before calling the resolve script: Use contact_search with query: "<name>" and channel_type: "slack". If a matching contact has externalUserId (Slack user ID) and externalChatId (DM channel ID), skip the API lookups and use those IDs directly with chat.postMessage via assistant oauth request --provider slack_channel.

   When contact_search returns notes for the recipient, use them to inform the message's tone, formality, and content. Contact notes capture relationship context and communication preferences that should shape how you write to this person.

2. After resolving via script: When you had to use slack-resolve.ts user or conversations.open to resolve a user, save the contact with contact_upsert so you can find them by name next time. External Slack IDs (user ID, DM channel ID) are cached automatically by the messaging layer and should not be passed through contact_upsert.

Privacy Rules

Channel privacy must be respected at all times:

• Check is_private on each channel before sharing content elsewhere
• Private channel content must NEVER be shared to other channels, DMs, or external destinations
• If the user asks to share private channel content, explain why you can't and offer alternatives (summarize the topic without quoting, ask the user to share manually)
• Public channel content can be shared with attribution ("From #channel: ...")
• Always confirm with the user before sending content to any destination

Threading

When responding to messages from Slack channels, replies should be threaded. Pass thread_ts to chat.postMessage to reply in a thread rather than posting a new top-level message:

assistant oauth request --provider slack_channel \
  -X POST \
  -d '{"channel":"C0123456789","text":"Replying in thread","thread_ts":"1716000000.000001"}' \
  /chat.postMessage --json

Connection

Before making any Slack API calls, verify that Slack is connected. If not connected, load the slack-app-setup skill (skill_load with skill: "slack-app-setup") and follow its guided flow. Do NOT improvise setup instructions -- the slack-app-setup skill is the single source of truth. Slack uses Socket Mode and does not require redirect URLs or any OAuth flow.

Error Handling

If a Slack API call fails due to missing or invalid credentials -- for example, an error indicating that the token is missing or invalid -- do NOT attempt to fix the credentials manually. Instead, load the slack-app-setup skill (skill_load with skill: "slack-app-setup") and follow its guided flow to set up or reconnect Slack. Tell the user something like "Slack needs to be reconnected" and start the setup skill.

Delivery Notes

• For rich content (digests, reports, formatted summaries): use chat.postMessage with blocks via assistant oauth request --provider slack_channel
• For short alerts: assistant notifications send via bash is fine -- it lets the notification router pick the best channel
• For scheduled tasks: always include an explicit Slack API call to deliver results, otherwise output only lives in the conversation log