The checks you run at 3am,
explained properly.
A reference for 67 network, DNS, TLS, email and security diagnostics. Not manual pages — what each check actually tells you, which failure it distinguishes from which, and what changes when it runs on a schedule instead of when you remember.
By what it interrogates
- 16 DNS & Domains Resolution, records, propagation and expiry.
- 5 TLS & Certificates Chains, ciphers, expiry and what browsers will accept.
- 11 Email Deliverability SPF, DKIM, DMARC, MX and reputation.
- 11 Network Path & Reachability Latency, loss, routing and whether the port is even open.
- 7 HTTP & Web Delivery Status, headers, timing and what the browser really got.
- 9 Security & Exposure What you are publishing that you did not mean to.
- 8 Addressing & Routing Subnets, address families, ownership and BGP.
Running them without you
Every check here is more useful on a schedule than in a terminal, because the interesting result is almost never the first one — it is the one that differs from last time.
- Scheduled Reporting for Infrastructure Teams A check you run by hand tells you about the moment you ran it. A check that runs on a schedule tells you when something changed — which is almost always the question you actually needed answered. Read →
- Synthetic Monitoring: Proving the Path Still Works Every layer you monitor can be green while the thing your users do is broken. Synthetic checks exercise the path end to end instead of asking each component whether it feels well. Read →
- Real User Monitoring for Operations Teams Synthetic checks tell you the platform works from where you tested. Real user data tells you whether it works where your users are, which is a question no amount of probing from your own datacentre answers. Read →
Playbooks
Sequences rather than single checks — the order to work a problem in when you have one data point and a phone that will not stop.
- Making a DNS Change Without Causing an Outage Lower the TTL days ahead, verify against resolvers rather than your own cache, and know what you will do if it goes wrong before you press save.
- Certificate Expiry: Building a Process That Does Not Fail Automated renewal removes the routine work and leaves a new failure mode: a process that has quietly stopped. Verification is what closes it.
- Email Deliverability Triage "Our email is going to spam" is a symptom with at least four unrelated causes. Working them in the right order saves days.
- Is It Down, Or Is It Just Me? Most outage reports arrive as one data point. Turning that into a location takes four or five checks, in a specific order.
These checks run on NetTests.NET
Everything described here is a live tool you can point at your own hosts, and every one of them can be put on a schedule with results kept, compared and alerted on. This site explains the checks; NetTests.NET runs them.