Dimension scores are derived from public data and fields; weighted into the composite. Reference only.
Certificate Expiry Monitor is a lightweight tool for managing the lifecycle of website SSL/TLS certificates. After users enter one or more domain names and an email address, the service continuously checks certificate expiration dates and sends email reminders before and after expiry, reducing the risk of HTTPS failures caused by forgotten renewals.
Its scope is very clear: monitor certificate validity, send email alerts, detect unreachable sites, and check the certificate chain. Reminder points include 90, 60, 30, 14, 7, 5, 3, 2, and 1 day before expiry, the day of expiry, plus 2 and 7 days after expiry, making it suitable for operations workflows that need multiple early warnings. Certificate checks run at least once every 2 days, and usually daily. The tool also checks up to 10 certificates in the certificate chain, so it does not only focus on the site’s leaf certificate, but can also detect expired intermediate or chain certificates.
The project is fully open-source software, licensed under GNU AGPLv3 or later. The official service is free and allows adding any number of domains, although the page warns users not to abuse it; excessive usage may require separate discussion. The official site clearly states that the service is provided on a best-effort basis and does not guarantee uptime. If 100% availability is required, users can deploy their own instance. This makes it especially suitable for technically capable teams that want control over their own monitoring pipeline.
Its advantages are that it is free, simple, and requires no complex configuration—users only need to fill in a form with domains and an email address. The reminder policy is detailed, and certificate chain checks are supported. The limitations are also clear: the description does not show support for APIs, SDKs, webhooks, Slack, SMS, or other integrations, nor does it mention team permissions, reports, SLAs, or audit features. For enterprise-grade observability platforms, it is more of a dedicated small utility than a complete monitoring system.
It is suitable for individual webmasters, small teams, developers, and operations staff who need to monitor certificate expiry risks for official websites, APIs, client projects, and similar services. The source text does not provide information about access from China, so this should be considered unknown. If access or email delivery is unstable, self-hosting may be a good option, or alternatives such as UptimeRobot, Better Stack, Prometheus Blackbox Exporter, and Healthchecks.io can be considered.
⚠ This review is compiled from public sources and does not constitute a purchase recommendation. Verify all facts on the vendor's official site. Verify on sslmonitor.nl official site.
sslmonitor.nl is an Netherlands Dev Tools provider. TG4G tracks its product information, an overall rating of 7.0/10, and a China-accessibility score of China direct-connect friendly. Click "Visit Official Site" to reach sslmonitor.nl directly.