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

Create app: https://api.slack.com/apps
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

Install to Workspace
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

Syntax	Result
`bold`	bold
`_italic_`	italic
`~strike~`	~~strike~~
`code`	`code`
`<URL\|text>`	hyperlink
`<@U123>`	@mention user
`<#C123>`	#channel link

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