# Domain Expiry Reminder
URL: /docs/experiments/domain-expiry-reminder
> Track domain RDAP and TLS certificate expiry in D1 with daily cron emails at 30/7/1 days - domain and cert monitoring
Tags: network, monitoring, tls, rdap, email, cron, certificates
Bindings: D1, CRON, EMAIL
Markdown: /llms.mdx/experiments/domain-expiry-reminder/content.md
Never let a domain or TLS certificate expire. Registration expiry comes from **RDAP**, certificate expiry from **Certificate Transparency** logs, watched domains live in **D1**, and a daily **Cron Trigger** emails reminders through the `send_email` binding.
## Features [#features]
* Registration expiry via RDAP: IANA bootstrap (`data.iana.org/rdap/dns.json`, cached in memory for 24h) → registry server, falling back to `rdap.org`
* TLS certificate expiry via [crt.sh](https://crt.sh) CT search: latest non-expired certificate whose names include the exact hostname
* Reminders at **30**, **7**, and **1** days left, each sent once per expiry date (deduped in a `reminders` table, so a renewal resets them)
* Partial results: a failing source returns `null` with a reason in `errors` instead of failing the request
* One-off `GET /lookup` without saving anything
## API Reference [#api-reference]
### POST /domains [#post-domains]
Watch a domain.
**`domain`** `string` (required)
Bare hostname such as `example.com` (no scheme, path, or port).
**`alertEmail`** `string` (required)
Where reminders are sent.
```bash
curl -X POST "https://your-worker.workers.dev/domains" \
-H "Content-Type: application/json" \
-d '{"domain":"example.com","alertEmail":"ops@example.com"}'
```
```json
{
"id": 1,
"domain": "example.com",
"alertEmail": "ops@example.com",
"createdAt": "2026-10-01T09:00:00.000Z"
}
```
### GET /domains/:id [#get-domainsid]
Runs a live check for a watched domain, stores the expiry dates on the row, and returns the record plus `status` (same shape as `/lookup`).
### DELETE /domains/:id [#delete-domainsid]
Stop watching a domain and delete its reminder history.
### GET /lookup [#get-lookup]
One-off check without saving.
**`domain`** `string` (required)
Bare hostname to check.
```bash
curl "https://your-worker.workers.dev/lookup?domain=example.com"
```
```json
{
"domain": "example.com",
"checkedAt": "2026-10-01T09:00:00.000Z",
"registration": {
"expiresAt": "2027-08-13T04:00:00.000Z",
"daysLeft": 315,
"registrar": "RESERVED-Internet Assigned Numbers Authority"
},
"certificate": null,
"errors": {
"certificate": "crt.sh: Request timed out"
}
}
```
#### Error Codes [#error-codes]
* `400` - `INVALID_BODY`, `INVALID_DOMAIN`, `INVALID_EMAIL`, `INVALID_ID`
* `404` - `NOT_FOUND`
* `500` - `INTERNAL_ERROR`
## How reminders work [#how-reminders-work]
The cron (`0 9 * * *`) loads every watched domain, checks both sources, and for each expiry finds the smallest threshold that days-left has crossed (`daysLeft <= 30` → 30, `<= 7` → 7, `<= 1` → 1). If no row exists in `reminders` for `(domain, kind, threshold, expiresAt)`, it sends the email and records it. A domain added with 5 days left gets the 7-day reminder only, then the 1-day reminder later. When the expiry date changes after a renewal, the thresholds apply again.
## Use Cases [#use-cases]
* Side-project domains spread across several registrars
* Catch certificates that silently stopped auto-renewing
* Learn D1 + Cron Triggers + `send_email` with a dedupe table
* Ad-hoc expiry checks from scripts via `GET /lookup`
## Limitations [#limitations]
* RDAP queries the hostname as given; pass the registrable domain (`example.co.uk`, not `www.example.co.uk`) for registration data
* Some ccTLDs have no RDAP service, so `registration` is `null`
* crt.sh is slow and frequently returns 5xx; requests time out after 10 seconds and the certificate comes back `null`
* CT logs show issued certificates, not the one your server is actually serving
* Domains are checked one after another in a single cron run, so very large lists can hit Worker time limits
## Use in your project [#use-in-your-project]
## Deployment [#deployment]
### Click the deploy button [#click-the-deploy-button]
[](https://deploy.workers.cloudflare.com/?url=https://github.com/shrinathsnayak/cloudflare-experiments/tree/main/apps/experiments/domain-expiry-reminder)
### Apply migrations and configure email [#apply-migrations-and-configure-email]
```bash
npx wrangler d1 migrations apply domain-expiry-reminder-db --remote
npx wrangler email sending enable yourdomain.com
```
Set `ALERT_FROM_EMAIL` in `wrangler.json` to an address on the onboarded domain.
### Test your deployment [#test-your-deployment]
```bash
curl "https://your-worker.workers.dev/lookup?domain=example.com"
```
## Local Development [#local-development]
```bash
cd apps/experiments/domain-expiry-reminder
npm install
npx wrangler d1 migrations apply domain-expiry-reminder-db --local
npx wrangler dev --test-scheduled
```
```bash
curl "http://localhost:8787/lookup?domain=example.com"
curl "http://localhost:8787/__scheduled?cron=0+9+*+*+*"
```
## Configuration [#configuration]
`wrangler.json` declares:
* **D1** `DB` (`migrations/0000_init.sql` creates `domains` and `reminders`)
* **`send_email` binding** `EMAIL`
* **Cron** `0 9 * * *`
* **Var** `ALERT_FROM_EMAIL`
## Cloudflare Features Used [#cloudflare-features-used]
* **[D1](https://developers.cloudflare.com/d1/)** - Watched domains and sent-reminder log
* **[Cron Triggers](https://developers.cloudflare.com/workers/configuration/cron-triggers/)** - Daily expiry checks
* **[Email Sending](https://developers.cloudflare.com/email-service/api/send-emails/workers-api/)** - `send_email` binding for reminders