Slack

Slack API

Send messages, read channels, and interact with Slack workspaces.

When to Use

• Send messages to channels or users
• Read channel message history
• Upload files to Slack
• List channels and users
• Add reactions to messages

Prerequisites

export SLACK_BOT_TOKEN=xoxb-your-bot-token

Get Token

1. Create app: https://api.slack.com/apps
2. Add Bot Token Scopes (OAuth & Permissions):

• chat:write - Send messages
• channels:read - List public channels
• channels:history - Read channel messages
• files:write - Upload files
• users:read - List users
• reactions:write - Add reactions

3. Install to Workspace
4. Copy "Bot User OAuth Token" (xoxb-...)

Important: When using $VAR in a command that pipes to another command, wrap the command containing $VAR in bash -c '...'. Due to a Claude Code bug, environment variables are silently cleared when pipes are used directly.

bash -c 'curl -s "https://api.example.com" -H "Authorization: Bearer $API_KEY"'

Core APIs

List Channels

bash -c 'curl -s -H "Authorization: Bearer $SLACK_BOT_TOKEN" "https://slack.com/api/conversations.list?types=public_channel"' | jq '.channels[] | {id, name}'

Docs: https://docs.slack.dev/reference/methods/conversations.list

Get Channel History

Replace <channel-id> with the actual channel ID:

bash -c 'curl -s -H "Authorization: Bearer $SLACK_BOT_TOKEN" "https://slack.com/api/conversations.history?channel=<channel-id>&limit=10"' | jq '.messages[] | {ts, user, text}'

Docs: https://docs.slack.dev/reference/methods/conversations.history

Send Message

Write to /tmp/request.json:

{
  "channel": "<channel-id>",
  "text": "Hello, World"
}

bash -c 'curl -s -X POST "https://slack.com/api/chat.postMessage" -H "Authorization: Bearer $SLACK_BOT_TOKEN" -H "Content-Type: application/json" -d @/tmp/request.json'

Docs: https://docs.slack.dev/reference/methods/chat.postmessage

Send with Blocks

Write to /tmp/request.json:

{
  "channel": "<channel-id>",
  "text": "Notification",
  "blocks": [
    {
      "type": "section",
      "text": {"type": "mrkdwn", "text": "*Alert:* Something happened"}
    },
    {
      "type": "section",
      "fields": [
        {"type": "mrkdwn", "text": "*Status:*\nActive"},
        {"type": "mrkdwn", "text": "*Priority:*\nHigh"}
      ]
    }
  ]
}

bash -c 'curl -s -X POST "https://slack.com/api/chat.postMessage" -H "Authorization: Bearer $SLACK_BOT_TOKEN" -H "Content-Type: application/json" -d @/tmp/request.json'

Block Kit Builder: https://app.slack.com/block-kit-builder

Reply in Thread

Write to /tmp/request.json:

{
  "channel": "<channel-id>",
  "thread_ts": "<thread-timestamp>",
  "text": "Thread reply"
}

bash -c 'curl -s -X POST "https://slack.com/api/chat.postMessage" -H "Authorization: Bearer $SLACK_BOT_TOKEN" -H "Content-Type: application/json" -d @/tmp/request.json'

Update Message

Write to /tmp/request.json:

{
  "channel": "<channel-id>",
  "ts": "<message-timestamp>",
  "text": "Updated message"
}

bash -c 'curl -s -X POST "https://slack.com/api/chat.update" -H "Authorization: Bearer $SLACK_BOT_TOKEN" -H "Content-Type: application/json" -d @/tmp/request.json'

Docs: https://docs.slack.dev/reference/methods/chat.update

Delete Message

Write to /tmp/request.json:

{
  "channel": "<channel-id>",
  "ts": "<message-timestamp>"
}

bash -c 'curl -s -X POST "https://slack.com/api/chat.delete" -H "Authorization: Bearer $SLACK_BOT_TOKEN" -H "Content-Type: application/json" -d @/tmp/request.json'

List Users

bash -c 'curl -s -H "Authorization: Bearer $SLACK_BOT_TOKEN" "https://slack.com/api/users.list"' | jq '.members[] | {id, name, real_name}'

Docs: https://docs.slack.dev/reference/methods/users.list

Get User by Email

Replace <user-email> with the actual email address:

bash -c 'curl -s -H "Authorization: Bearer $SLACK_BOT_TOKEN" "https://slack.com/api/users.lookupByEmail?email=<user-email>"'

Docs: https://docs.slack.dev/reference/methods/users.lookupbyemail

Upload File

curl -s -X POST 'https://slack.com/api/files.upload' -H "Authorization: Bearer $SLACK_BOT_TOKEN" -F 'channels=C1234567890' -F 'file=@/path/to/file.txt' -F 'title=My File'

Docs: https://docs.slack.dev/reference/methods/files.upload

Add Reaction

Write to /tmp/request.json:

{
  "channel": "<channel-id>",
  "timestamp": "<message-timestamp>",
  "name": "thumbsup"
}

bash -c 'curl -s -X POST "https://slack.com/api/reactions.add" -H "Authorization: Bearer $SLACK_BOT_TOKEN" -H "Content-Type: application/json" -d @/tmp/request.json'

Docs: https://docs.slack.dev/reference/methods/reactions.add

Message Formatting

Rate Limits

• Tier 1: 1 request/second
• Tier 2: 20 requests/minute
• Tier 3: 50 requests/minute
• Tier 4: 100 requests/minute

See: https://docs.slack.dev/apis/web-api/rate-limits

API Reference

• All Methods: https://docs.slack.dev/reference/methods
• Scopes: https://docs.slack.dev/reference/scopes
• Block Kit: https://docs.slack.dev/reference/block-kit
• App Management: https://api.slack.com/apps