Guides
Plain-language explanations of the things our tools measure: email, DNS, certificates, passwords, and what your browser gives away. Written to be read once and understood.
When to use a disposable email address
What a disposable email address is good for, where it will let you down, and how to decide which address a signup form deserves.
How email tracking pixels work
How a one-pixel image tells a sender when and where you opened their email, and the settings that stop it.
How to read email headers
A walk through the headers on a real message: who sent it, which servers handled it, and whether it passed authentication.
SPF, DKIM and DMARC explained
What the three email authentication records do, how they fit together, and how to read the ones on your own domain.
DNS record types explained
A, AAAA, CNAME, MX, TXT, NS, CAA, SOA and SRV: what each DNS record is for, with examples you can look up yourself.
Why DNS changes take time to show up
What DNS propagation really is, how TTLs and caches decide who sees your change, and how to plan a switch with no downtime.
What WHOIS and RDAP tell you about a domain
How domain registration data works, what is public and what is redacted, and how to read a lookup result.
What your IP address reveals about you
What a website can and cannot learn from your IP address, how accurate IP geolocation is, and what actually hides it.
Browser fingerprinting and how to reduce it
How websites recognize your browser without cookies, which signals matter most, and what realistically makes you harder to track.
What makes a password strong
Length, randomness and reuse: what actually protects a password, how attackers guess them, and how to check one against known breaches safely.
JSON Web Tokens explained
What is inside a JWT, why anyone can read it, how the signature works, and the mistakes that make tokens unsafe.
How TLS certificates work
What a TLS certificate proves, how the chain of trust is checked, and how to read the fields when a certificate looks wrong.
HTTP security headers worth setting
What each browser security header does, sensible starting values, and the order to roll them out without breaking your site.
Subnetting and CIDR notation
How to read an address like 10.0.4.0/22, work out the network, broadcast and host range, and split a network into smaller ones.