Automatic renewal fails more often than it should: a changed DNS record, a full disk or an expired API token, and the certificate quietly runs out. m0nitor reads the certificate on every HTTPS check and warns you days before browsers start to block your site.
Expiry warnings: Choose how early to hear about it: 7 days by default, adjustable up to a year ahead.
Checked on every run: The certificate is read with every HTTPS check, so a broken renewal shows up within minutes, not at the next weekly scan.
Separate alerts: "Certificate expiring" and "certificate expired" are their own events, so you can send them to a different channel than downtime.
From several regions: Checks run from several probe locations, which also catches regional differences behind CDNs and load balancers.
Why certificates still expire with auto-renewal
Let's Encrypt and similar services renew certificates automatically, but the renewal depends on a chain of things that can break: the ACME client, DNS validation records, firewall rules for the HTTP challenge, API credentials for your DNS provider and the reload of the web server after renewal.
When one link breaks, nothing tells you. The old certificate keeps working until the day it does not, and then visitors see a full-page browser warning instead of your site.
What m0nitor checks
Days until the certificate expires, with a warning window you choose
An expired certificate, which counts as an outage because browsers refuse the connection
Certificate problems reported by the probes, such as an untrusted chain or a hostname mismatch
Response status, response time and keywords on the same HTTPS check
Set up in three steps
Add an HTTPS monitor: Paste the URL of your site or API. Certificate checks are part of every HTTPS monitor.
Pick the warning window: Keep 7 days or choose how many days before expiry you want to hear about it.
Choose who is told: Email is ready on the free plan; paid plans add Slack, Teams, Discord, Telegram, PagerDuty and SMS.
Plan availability
SSL monitoring is part of every HTTPS monitor, including the free plan with 20 monitors and email alerts.
Related pages
Free SSL checker: Check any certificate once, without an account
Yes. Every HTTPS monitor checks the certificate, and the free plan includes 20 monitors with email alerts.
How early am I warned?
7 days before expiry by default. You can set the warning window per monitor, up to 365 days.
What is the difference to the SSL checker?
The SSL checker inspects a certificate once, when you ask. SSL monitoring checks it continuously and alerts you when something changes.
Does m0nitor check certificates behind a CDN?
It checks the certificate that the public hostname serves, which is the one your visitors see, including certificates served by Cloudflare and other CDNs.