Checks

A check is one thing that ZeroDrop monitors. Every active location probes it on a fixed interval. There are two types: HTTP/HTTPS and SMTP. This page describes every setting. To learn how results become an up or down verdict, see Consensus & status.

Settings for both types

Setting	Default	Notes
Name	required	A label for the check. It must be unique in your account.
Enabled	on	Turn a check off to stop the probes. The check is not deleted.
Interval	60 s	How often each location probes. The minimum is 60 seconds.
Timeout	5 s	A probe that takes more time than this is a failure.
Locations	all	Every check runs from all active locations. There is no selector for each check.
Public badges	off	Publish status, uptime and SSL badges for this check. See Dashboards.

Your account has a maximum number of checks and a minimum interval. The Settings page shows both. You can ask for an increase.

HTTP / HTTPS checks

An HTTP check requests a URL. The response decides success or failure.

Setting	Default	Notes
URL	required	The full `http(s)://` URL to request.
Method	`GET`	Any standard HTTP method.
Expected status	`200`	If the final response status is different, the probe fails.
Body pattern	none	Optional text that must occur in the response body.
Follow redirects	on	When off, a `3xx` response is the final response. Use this to test a redirect.
Max redirects	5	The number of hops to follow before the probe stops.

TLS certificate settings (HTTPS)

For https:// URLs you can also control how ZeroDrop treats the certificate.

Setting	Default	Notes
SSL certificate must validate	on	The certificate of the server must chain to a trusted root and match the host. Turn this off to monitor a host with a self-signed or untrusted certificate.
Fail when fewer days left than	7 days	The check fails when the certificate has fewer days of validity than this number. ZeroDrop therefore alerts you before the certificate expires. To ignore expiry, set this to Off.

On every probe ZeroDrop also records:

The DNS time, the time to first byte (TTFB) and the total latency.
The response size in bytes.
For HTTPS, the TLS certificate chain: the issuer, the subject and the days until expiry. You can then find a certificate that expires soon.

Examples

Health endpoint: GET https://api.example.com/healthz, expected status 200, body pattern ok.
Test a redirect: GET http://example.com, follow redirects off, expected status 301.
Authenticated API: GET https://api.example.com/v1/models, expected status 401. A 401 response proves that the API runs and enforces authentication.

SMTP checks

An SMTP check connects to a mail server. It reads the welcome banner and measures the time that the banner took to arrive.

Setting	Default	Notes
Host	required	The hostname of the mail server.
Port	25	Common values: `25` (inbound MX) and `587` (submission).
STARTTLS	on	When on, ZeroDrop sends `EHLO` and `STARTTLS`, then examines the TLS certificate.
Expected banner	none	Optional text that must occur in the `220` greeting.

The TLS certificate settings for HTTPS also apply to the certificate from STARTTLS.

Setting	Default	Notes
SSL certificate must validate	on	The STARTTLS certificate must chain to a trusted root and match the host. Turn it off for self-signed mail servers.
Fail when fewer days left than	7 days	ZeroDrop alerts you before the certificate of the mail server expires. To ignore expiry, set this to Off.

The probe succeeds when the server answers with a 220 greeting. If you entered a banner pattern, the banner must also match. If STARTTLS is on, the negotiation must succeed and the certificate must pass the settings in the table. The main metric for an SMTP check is the welcome time: how quickly the banner arrived.

Edit and delete a check

You can change any setting on a check at any time. The new settings apply on the next interval. If you delete a check, ZeroDrop removes it from every location and stops all of its alerts. The console asks you to confirm first.