Slack Messaging

Slack messaging — send messages, manage channels, upload files, add reactions, and automate team notifications via CLI and API.

Slack Integration

Send messages, manage channels, upload files, and automate notifications in Slack workspaces using the Web API. Works with bot tokens or user tokens.

Setup

# 1. Create a Slack App: https://api.slack.com/apps → Create New App
# 2. Add scopes under OAuth & Permissions:
#    Bot Token Scopes: chat:write, channels:read, channels:history,
#                      files:write, reactions:write, users:read
# 3. Install to workspace → copy Bot User OAuth Token

export SLACK_TOKEN="xoxb-..."   # Bot token (starts with xoxb-)

For user-level actions (DMs to yourself, custom status), use a User OAuth Token (xoxp-...) instead.

Sending Messages

# Simple text message
curl -s -X POST https://slack.com/api/chat.postMessage \
  -H "Authorization: Bearer $SLACK_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C0123ABCDEF", "text": "Deploy complete ✓"}'

# With rich formatting (Block Kit)
curl -s -X POST https://slack.com/api/chat.postMessage \
  -H "Authorization: Bearer $SLACK_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{
    "channel": "C0123ABCDEF",
    "blocks": [
      {"type": "header", "text": {"type": "plain_text", "text": "Deploy Report"}},
      {"type": "section", "text": {"type": "mrkdwn", "text": "*Status:* ✅ Success\n*Version:* v2.1.0\n*Duration:* 45s"}}
    ]
  }'

# Reply in thread
curl -s -X POST https://slack.com/api/chat.postMessage \
  -H "Authorization: Bearer $SLACK_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C0123ABCDEF", "thread_ts": "1234567890.123456", "text": "Fix deployed"}'

# Schedule a message (Unix timestamp)
curl -s -X POST https://slack.com/api/chat.scheduleMessage \
  -H "Authorization: Bearer $SLACK_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C0123ABCDEF", "text": "Standup time!", "post_at": 1700000000}'

# Update a message
curl -s -X POST https://slack.com/api/chat.update \
  -H "Authorization: Bearer $SLACK_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C0123ABCDEF", "ts": "1234567890.123456", "text": "Updated text"}'

Channels

# List channels (paginated — follow next_cursor)
curl -s "https://slack.com/api/conversations.list?types=public_channel,private_channel&limit=200" \
  -H "Authorization: Bearer $SLACK_TOKEN" | jq '.channels[] | {id, name, num_members}'

# Get channel info
curl -s "https://slack.com/api/conversations.info?channel=C0123ABCDEF" \
  -H "Authorization: Bearer $SLACK_TOKEN"

# Channel history (recent messages)
curl -s "https://slack.com/api/conversations.history?channel=C0123ABCDEF&limit=10" \
  -H "Authorization: Bearer $SLACK_TOKEN" | jq '.messages[] | {ts, text, user}'

# Find channel by name
curl -s "https://slack.com/api/conversations.list?types=public_channel&limit=999" \
  -H "Authorization: Bearer $SLACK_TOKEN" | jq '.channels[] | select(.name=="general") | .id'

# Create a channel
curl -s -X POST https://slack.com/api/conversations.create \
  -H "Authorization: Bearer $SLACK_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"name": "incident-2026-04", "is_private": false}'

# Set channel topic
curl -s -X POST https://slack.com/api/conversations.setTopic \
  -H "Authorization: Bearer $SLACK_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C0123ABCDEF", "topic": "Production incident — DB latency spike"}'

Files

# Upload a file (v2 API)
curl -s -X POST https://slack.com/api/files.getUploadURLExternal \
  -H "Authorization: Bearer $SLACK_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"filename": "report.csv", "length": 1024}' \
  | jq '{upload_url, file_id}'
# Then POST the file content to upload_url, then call files.completeUploadExternal

# Share a remote file link
curl -s -X POST https://slack.com/api/files.remote.add \
  -H "Authorization: Bearer $SLACK_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"external_id": "report-1", "external_url": "https://example.com/report.pdf", "title": "Monthly Report"}'

Reactions & Users

# Add reaction to a message
curl -s -X POST https://slack.com/api/reactions.add \
  -H "Authorization: Bearer $SLACK_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"channel": "C0123ABCDEF", "timestamp": "1234567890.123456", "name": "white_check_mark"}'

# List users
curl -s "https://slack.com/api/users.list?limit=200" \
  -H "Authorization: Bearer $SLACK_TOKEN" | jq '.members[] | {id, name, real_name}'

# User info by ID
curl -s "https://slack.com/api/users.info?user=U0123ABCDEF" \
  -H "Authorization: Bearer $SLACK_TOKEN" | jq '.user | {name, real_name, tz}'

# Look up user by email
curl -s "https://slack.com/api/users.lookupByEmail?email=[e-mail]" \
  -H "Authorization: Bearer $SLACK_TOKEN" | jq '.user.id'

Common Workflows

CI/CD notification: After a deploy, post a formatted message to #deployments with version, commit, and status. On failure, create a thread with the error log.

Incident channel: Create a private channel named incident-YYYY-MM-DD-<slug>, set the topic, invite responders, post the initial report with severity and affected services.

Standup reminder: Schedule a daily message at 9:30 AM to #team with a prompt template. Collect threaded replies.

Error alert: When Sentry fires a webhook, post the error title, count, and link to the relevant channel. Add a 🔴 reaction for critical, 🟡 for warning.

Notes

• Bot tokens (xoxb-) can only post to channels the bot has been invited to
• Rate limits: ~1 msg/sec per channel (Tier 2); respect Retry-After headers
• Channel IDs (not names) are required for most API calls — look them up first
• For rich messages, use Block Kit Builder to design layouts
• mrkdwn (Slack's markdown) uses *bold*, _italic_, ~strike~, `code`, >quote
• DMs: use conversations.open with user IDs to get the DM channel ID, then post normally