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"' | jq .

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

bash -c 'curl -s -H "Authorization: Bearer $SLACK_BOT_TOKEN" '"'"'https://slack.com/api/conversations.history?channel=C1234567890&limit=10'"'"'' | jq '.messages[] | {ts, user, text}

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

Send Message

curl -s -X POST 'https://slack.com/api/chat.postMessage' -H "Authorization: Bearer $SLACK_BOT_TOKEN" -H 'Content-Type: application/json' -d @- << 'EOF'
{"channel":"C1234567890","text":"Hello, World"}
EOF

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

Send with Blocks

curl -s -X POST 'https://slack.com/api/chat.postMessage' -H "Authorization: Bearer $SLACK_BOT_TOKEN" -H 'Content-Type: application/json' -d @- << 'EOF'
{
  "channel": "C1234567890",
  "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"}
  ]
  }
  ]
}
EOF

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

Reply in Thread

curl -s -X POST 'https://slack.com/api/chat.postMessage' -H "Authorization: Bearer $SLACK_BOT_TOKEN" -H 'Content-Type: application/json' -d @- << 'EOF'
{"channel":"C1234567890","thread_ts":"1234567890.123456","text":"Thread reply"}
EOF

Update Message

curl -s -X POST 'https://slack.com/api/chat.update' -H "Authorization: Bearer $SLACK_BOT_TOKEN" -H 'Content-Type: application/json' -d @- << 'EOF'
{"channel":"C1234567890","ts":"1234567890.123456","text":"Updated message"}
EOF

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

Delete Message

curl -s -X POST 'https://slack.com/api/chat.delete' -H "Authorization: Bearer $SLACK_BOT_TOKEN" -H 'Content-Type: application/json' -d @- << 'EOF'
{"channel":"C1234567890","ts":"1234567890.123456"}
EOF

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

curl -s -H "Authorization: Bearer $SLACK_BOT_TOKEN" 'https://slack.com/api/users.lookupByEmail?email=user@example.com'

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

curl -s -X POST 'https://slack.com/api/reactions.add' -H "Authorization: Bearer $SLACK_BOT_TOKEN" -H 'Content-Type: application/json' -d @- << 'EOF'
{"channel":"C1234567890","timestamp":"1234567890.123456","name":"thumbsup"}
EOF

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