Build Dead Man's Snitch

YESreplaces $19/mosaves $228/yrback to the verdict

0%0 of 17 items done

Saved on this device only. Tick prerequisites first, then work the phases in order · do not start one until the checks above it pass.

A dead-man's switch for scheduled jobs: each job checks in at a URL, silence past the interval plus grace raises one alert, the next check-in recovers it. The minimal version of heartbeat monitoring, on a box that is not the one running the jobs.

estimated effort one sittingthe files for this build are in the project pack

RuntimeNode 22, node:http and node:sqliteHostingA VPS separate from the jobs

Before step 1

Everything below is assumed from the first step. Tick each one when you actually have it, not when you plan to.

installfree
Why Everything in this build runs on it: the server, the scripts, the tests.
Get it Download the LTS installer from nodejs.org, or install with your package manager (brew install node, or nvm install 22). Restart the terminal afterwards. open ↗
Verify node --version prints v22 or higher
installfree
Why Every step below is a command you type or a file you edit.
Get it VS Code (code.visualstudio.com), Cursor or Zed. Open a folder for the project and use the editor's built-in terminal. open ↗
Verify You can open a folder and run a command in its terminal
installfree
Why History for your code, and the way most hosts deploy.
Get it Install from git-scm.com or with your package manager, then run git init in the project folder once it exists. open ↗
Verify git --version prints a version
API keyfree
Why Alerts go to a chat channel you already watch. A webhook URL is the only credential this needs.
Get it Discord: Server settings > Integrations > Webhooks > New Webhook, copy the URL. Slack: create an app at api.slack.com/apps, enable Incoming Webhooks, add to a channel, copy the URL. Telegram: create a bot with @BotFather and use the bot token plus your chat id. open ↗
Verify curl -X POST -H 'Content-Type: application/json' -d '{"content":"test"}' <url> posts a message (Discord form; Slack uses a text field)
have readyfree
Why Interval plus grace per snitch.
Get it crontab -l and a list.
accountabout $5 a month
Why This needs one process running all the time with a public address. Separate from the jobs it watches.
Get it Hetzner Cloud (from about 4 EUR), DigitalOcean or Fly.io. Ubuntu 24.04, the smallest size. You need SSH access and a public IP. Only needed for the deploy phase; develop locally first. open ↗
installfree
Why Automatic HTTPS in front of the Node process. Without TLS the browser features this relies on (and your visitors' trust) do not work.
Get it On the VPS: follow the install steps at caddyserver.com/docs/install for Ubuntu. One Caddyfile with your domain and a reverse_proxy line is the whole config. open ↗
Verify caddy version prints a version on the server

Data model

Create these before the first phase that stores anything. Changing a table later is the expensive kind of change.

- snitches: id (uuid), name, interval_seconds, grace_seconds, status ('waiting' | 'healthy' | 'missing' | 'paused'), last_checkin_at
- checkins: id, snitch_id, received_at, ok (bool), note
- alerts: id, snitch_id, kind ('missing' | 'recovered'), sent_at, error

UTC epoch milliseconds everywhere.

Environment variables

These go in a .env file the app reads at startup. The pack's .env.example is this table as a file · copy it, never commit the filled-in version.

Variable	Needed	Example	Where the value comes from
`PORT`	required	`3000`	Any free port.
`DATABASE_PATH`	required	`./data/snitches.db`	SQLite file.
`ALERT_WEBHOOK_URL`secret	required	`https://...`	Chat webhook.
`ALERT_FORMAT`	required	`slack`	discord, slack or telegram.
`SITE_URL`	required	`https://snitch.yourdomain.com`	Public base URL.
`ADMIN_USER`	required	`admin`	Any username for the basic-auth admin pages.
`ADMIN_PASS`secret	required	`change-me-to-a-long-random-string`	Generate one: openssl rand -base64 24. Never reuse a real password.

The build, in order

1
Check-ins
GET, POST or HEAD /s/:uuid records a check-in; /fail records a failure; unknown ids 404.
1. snitches (id, name, interval_seconds, grace_seconds, status, last_checkin_at), checkins (id, snitch_id, received_at, ok, note), alerts.
  terminal
  mkdir snitch && cd snitch && git init && npm init -y && npm pkg set type=module mkdir -p data && cp .env.example .env
done when · tick each as it passes
next phase
2
The switch
healthy within interval plus grace, missing beyond, fail flips immediately.
done when · tick each as it passes
next phase
3
Shouting
One message missing, one recovered.
done when · tick each as it passes
next phase
4
Admin
Create, pause, delete; copy the URL and the crontab line.
done when · tick each as it passes
next phase
5
Deploy
HTTPS, a service, retention, README.
2. Files README.md
done when · tick each as it passes
next phase
6
Operate it like a productproduct builder
Only for the product-builder path: know when the switch is down, never lose the database, and keep the server patched.
1. Answer 200 with the build id and a quick database read. Point a free uptime monitor (or your own, from the Healthchecks entry on this site) at it so an outage is noticed before a user notices.
2. One JSON line per request: method, path, status, duration, no raw IPs. Rotate weekly with logrotate, keep eight.
3. SQLite's .backup command makes a consistent copy while the app runs. Copy it to object storage or a second machine; then, once, restore it into a fresh checkout and confirm the app reads it.
  terminal
  sqlite3 data/app.db ".backup '/tmp/app-$(date +%F).db'" rclone copy /tmp/app-$(date +%F).db remote:backups/
4. Firewall allowing only 22, 80 and 443; unattended security updates on; the app running as an unprivileged user under systemd with Restart=on-failure.
done when · tick each as it passes

what this build does not replace

Smart alerts that parse output, PagerDuty and Heroku integrations, team accounts.
the off-box vantage point
smart alerts and error-notice parsing
the integrations (PagerDuty, Slack app, Heroku add-on)
unlimited team members on one account

after v1, if you want it

A weekly summary message of every snitch's health

Need the files? The project pack on the verdict page hands your agent the whole brief · more cron monitoring.