Seppo — Slack Bot on Cloudflare Workers

Seppo is a Slack bot powered by Claude AI, deployed as a Cloudflare Worker. When mentioned in a Slack channel, Seppo responds in character as a helpful 60-year-old Finnish caretaker.

Prerequisites

• Cloudflare account with Workers enabled
• Anthropic API key
• Slack workspace with permission to create apps
• Node.js 18+ and npm

1. Create a Slack App

1. Go to api.slack.com/apps and click Create New App > From scratch.
2. Give it a name (e.g. Seppo) and select your workspace.
3. Under OAuth & Permissions, add the following Bot Token Scopes:
   • app_mentions:read
   • chat:write
4. Under Event Subscriptions, enable events and add the bot event app_mention. The Request URL will be set after deployment — come back to this step.
5. Install the app to your workspace and copy the Bot User OAuth Token (xoxb-...).
6. From Basic Information, copy the Signing Secret.

2. Set Up the Project

git clone <repo-url>
cd slack-bot-seppo
npm install

3. Configure wrangler.toml

Edit wrangler.toml and set your Cloudflare account ID:

name = "350fi-seppo"
main = "src/index.ts"
compatibility_date = "2025-02-14"
account_id = "<your-cloudflare-account-id>"
workers_dev = true

Your account ID is found in the Cloudflare dashboard URL or under Workers & Pages > Overview.

4. Add Secrets

Store sensitive values as Cloudflare Worker secrets (they are never stored in code or wrangler.toml):

# Slack bot token (xoxb-...)
npx wrangler secret put SLACK_BOT_TOKEN

# Slack signing secret
npx wrangler secret put SLACK_SIGNING_SECRET

# Anthropic API key
npx wrangler secret put ANTHROPIC_API_KEY

Each command will prompt you to paste the value.

5. Deploy

npm run deploy

Wrangler will output the Worker URL, e.g.:

https://350fi-seppo.<your-subdomain>.workers.dev

6. Finish Slack App Configuration

1. Go back to your Slack app's Event Subscriptions page.
2. Set the Request URL to your Worker URL. Slack will send a challenge request — the Worker handles it automatically.
3. Save changes and reinstall the app if prompted.

Local Development

Run the Worker locally with a tunnel for Slack events:

npm run dev

Wrangler starts a local server and can expose it via --remote or you can use a tunnel tool (e.g. cloudflared) to expose the local port to the internet for Slack's event delivery.

How It Works

Component	Role
slack-cloudflare-workers	Handles Slack request verification and event routing
Cloudflare Workers	Serverless runtime — no server to manage
Anthropic API	Generates Seppo's responses via claude-sonnet-4-5

When Seppo is @mentioned in a channel, the Worker:

1. Verifies the request signature from Slack
2. Strips the mention tag from the message text
3. Sends the text to Claude with Seppo's Finnish caretaker system prompt
4. Posts the reply in the same thread

Environment Variables

Variable	Source	Description
SLACK_BOT_TOKEN	Slack app	Bot User OAuth Token (xoxb-...)
SLACK_SIGNING_SECRET	Slack app	Used to verify request signatures
ANTHROPIC_API_KEY	Anthropic console	API key for Claude