Slack Bot

Slack Bot

Send messages and rich content to Slack channels using Incoming Webhooks or the Slack Web API. Build formatted announcements, marketing reports, metrics dashboards, and community updates with Block Kit.

Prerequisites

Requires either SLACK_WEBHOOK_URL or SLACK_BOT_TOKEN set in .env, .env.local, or ~/.claude/.env.global.

source ~/.claude/.env.global 2>/dev/null
source .env 2>/dev/null
source .env.local 2>/dev/null

if [ -n "$SLACK_WEBHOOK_URL" ]; then
  echo "SLACK_WEBHOOK_URL is set. Webhook mode available."
elif [ -n "$SLACK_BOT_TOKEN" ]; then
  echo "SLACK_BOT_TOKEN is set. Web API mode available."
else
  echo "Neither SLACK_WEBHOOK_URL nor SLACK_BOT_TOKEN is set."
  echo "See the Setup Guide below to configure Slack credentials."
fi

If neither variable is set, instruct the user to follow the Setup Guide section below.

Setup Guide

Option A: Incoming Webhook (Simple)

Incoming Webhooks are the fastest way to post messages. They require no OAuth scopes and are scoped to a single channel.

1. Go to https://api.slack.com/apps and click Create New App > From scratch.
2. Name the app (e.g., "Marketing Bot") and select your workspace.
3. In the left sidebar, click Incoming Webhooks and toggle it On.
4. Click Add New Webhook to Workspace at the bottom.
5. Select the channel to post to and click Allow.
6. Copy the Webhook URL (starts with https://hooks.slack.com/services/...).
7. Add it to your environment:

echo 'SLACK_WEBHOOK_URL=https://hooks.slack.com/services/T.../B.../xxxx' >> .env

Limitations: One webhook per channel. Cannot read messages, list channels, or reply to threads programmatically (you must know the thread_ts from a prior API response).

Option B: Bot Token (Full Featured)

Bot tokens give access to the full Slack Web API: post to any channel the bot is in, reply to threads, list channels, upload files, and more.

1. Go to https://api.slack.com/apps and click Create New App > From scratch.
2. Name the app and select your workspace.
3. In the left sidebar, click OAuth & Permissions.
4. Under Bot Token Scopes, add these scopes:

• chat:write - Post messages
• chat:write.public - Post to channels without joining
• channels:read - List public channels
• files:write - Upload files (optional, for images/reports)
• reactions:write - Add emoji reactions (optional)

1. Click Install to Workspace at the top and authorize.
2. Copy the Bot User OAuth Token (starts with xoxb-).
3. Add it to your environment:

echo 'SLACK_BOT_TOKEN=xoxb-your-token-here' >> .env

1. Invite the bot to the channels it should post in: type /invite @YourBotName in each channel.

Optional: Set a default channel for convenience:

echo 'SLACK_DEFAULT_CHANNEL=#marketing' >> .env

Method 1: Incoming Webhooks

Send a Simple Text Message

curl -s -X POST "$SLACK_WEBHOOK_URL" \
  -H "Content-Type: application/json" \
  -d '{
    "text": "Hello from the marketing bot!"
  }'

Send a Message with Username and Icon Override

curl -s -X POST "$SLACK_WEBHOOK_URL" \
  -H "Content-Type: application/json" \
  -d '{
    "text": "New blog post published!",
    "username": "Marketing Bot",
    "icon_emoji": ":mega:"
  }'

Send a Message with Block Kit (Webhook)

curl -s -X POST "$SLACK_WEBHOOK_URL" \
  -H "Content-Type: application/json" \
  -d '{
    "blocks": [
      {
        "type": "header",
        "text": {
          "type": "plain_text",
          "text": "New Product Launch"
        }
      },
      {
        "type": "section",
        "text": {
          "type": "mrkdwn",
          "text": "*Product X* is now live! Check out the announcement."
        }
      },
      {
        "type": "divider"
      },
      {
        "type": "section",
        "text": {
          "type": "mrkdwn",
          "text": "Read the full announcement on our blog."
        },
        "accessory": {
          "type": "button",
          "text": {
            "type": "plain_text",
            "text": "Read More"
          },
          "url": "https://example.com/blog/launch"
        }
      }
    ]
  }'

Method 2: Slack Web API (Bot Token)

The Web API provides full control over message delivery, threading, channel management, and more.

API Base

All requests go to https://slack.com/api/ with the header Authorization: Bearer {SLACK_BOT_TOKEN}.

Post a Message to a Channel

curl -s -X POST "https://slack.com/api/chat.postMessage" \
  -H "Authorization: Bearer ${SLACK_BOT_TOKEN}" \
  -H "Content-Type: application/json" \
  -d '{
    "channel": "#marketing",
    "text": "Weekly metrics report is ready!",
    "blocks": [
      {
        "type": "header",
        "text": {
          "type": "plain_text",
          "text": "Weekly Marketing Metrics"
        }
      },
      {
        "type": "section",
        "text": {
          "type": "mrkdwn",
          "text": "Here are the numbers for this week."
        }
      }
    ]
  }'

The response includes a ts (timestamp) field which identifies the message. Save this value for threading replies:

# Post and capture the message timestamp for threading
RESPONSE=$(curl -s -X POST "https://slack.com/api/chat.postMessage" \
  -H "Authorization: Bearer ${SLACK_BOT_TOKEN}" \
  -H "Content-Type: application/json" \
  -d '{
    "channel": "#marketing",
    "text": "Thread parent message"
  }')

MESSAGE_TS=$(echo "$RESPONSE" | python3 -c "import json,sys; print(json.load(sys.stdin).get('ts',''))")
echo "Message timestamp: $MESSAGE_TS"

Reply to a Thread

Use the thread_ts parameter to reply inside an existing thread:

curl -s -X POST "https://slack.com/api/chat.postMessage" \
  -H "Authorization: Bearer ${SLACK_BOT_TOKEN}" \
  -H "Content-Type: application/json" \
  -d "{
    \"channel\": \"#marketing\",
    \"thread_ts\": \"${MESSAGE_TS}\",
    \"text\": \"This is a threaded reply with additional details.\"
  }"

To also broadcast the reply to the channel (so it appears in the main conversation as well), add "reply_broadcast": true.

Update an Existing Message

curl -s -X POST "https://slack.com/api/chat.update" \
  -H "Authorization: Bearer ${SLACK_BOT_TOKEN}" \
  -H "Content-Type: application/json" \
  -d "{
    \"channel\": \"#marketing\",
    \"ts\": \"${MESSAGE_TS}\",
    \"text\": \"Updated message content.\",
    \"blocks\": []
  }"

Delete a Message

curl -s -X POST "https://slack.com/api/chat.delete" \
  -H "Authorization: Bearer ${SLACK_BOT_TOKEN}" \
  -H "Content-Type: application/json" \
  -d "{
    \"channel\": \"#marketing\",
    \"ts\": \"${MESSAGE_TS}\"
  }"

List Public Channels

Useful for discovering which channel to post to:

curl -s "https://slack.com/api/conversations.list?types=public_channel&limit=100" \
  -H "Authorization: Bearer ${SLACK_BOT_TOKEN}" | \
  python3 -c "
import json, sys
data = json.load(sys.stdin)
for ch in data.get('channels', []):
    members = ch.get('num_members', 0)
    print(f\"#{ch['name']}  |  Members: {members}  |  ID: {ch['id']}\")
"

Upload a File to a Channel

curl -s -X POST "https://slack.com/api/files.uploadV2" \
  -H "Authorization: Bearer ${SLACK_BOT_TOKEN}" \
  -F "file=@report.pdf" \
  -F "filename=weekly-report.pdf" \
  -F "channel_id=C0123456789" \
  -F "initial_comment=Here is this week's marketing report."

Add an Emoji Reaction

curl -s -X POST "https://slack.com/api/reactions.add" \
  -H "Authorization: Bearer ${SLACK_BOT_TOKEN}" \
  -H "Content-Type: application/json" \
  -d "{
    \"channel\": \"C0123456789\",
    \"timestamp\": \"${MESSAGE_TS}\",
    \"name\": \"white_check_mark\"
  }"

Slack Block Kit Reference

Block Kit is Slack's UI framework for building rich, interactive messages. Messages are composed