Tutorials

Guides that go beyond a single result, covering how DNS, SSL and hashing actually work, and what to do when something looks wrong. Paired with the free tools on Frabs, so you can read the explanation and run the check side by side.

Looking for a specific check instead? Browse all tools.

How DNS Records WorkWhat actually happens between typing a domain and a page loading, and what each record type in a DNS Lookup result is telling you.7 min read Pointing a Domain to a New Host Without Breaking AnythingA practical order of operations for moving a domain to a new server or provider, including the mistakes that cause avoidable downtime.6 min read Diagnosing DNS Problems When a Site Will Not ResolveA checklist for working through domain resolution failures in a sensible order, from a straightforward typo to an expired registration.6 min read Reading an SSL Certificate, Field by FieldWhat the common name, issuer, validity dates and chain of trust in a certificate actually mean, and how to read them in an SSL Checker result.7 min read Why Your SSL Certificate Might Show as InvalidThe five most common reasons a certificate fails validation, and a sensible order to check them in rather than guessing.6 min read HTTPS and TLS, What the Padlock Is Actually Telling YouWhat encryption in transit protects against, what it does not, and why a valid certificate and a security header check both matter.6 min read What a Checksum Hash Actually ProvesThe difference between hashing and encryption, what one way and collision resistant actually mean, and where hashes show up day to day.6 min read Verifying a Downloaded File with a HashHow to check a download has not been corrupted or tampered with, using commands available on macOS, Windows and Linux.5 min read MD5 Versus SHA-1 Versus SHA-256, and Why the Choice MattersWhat actually changed between these three widely used hash algorithms, and when each one is still an appropriate choice today.5 min read SPF Records ExplainedHow a domain publishes which servers are allowed to send email on its behalf, and how to read the syntax of a real SPF record.6 min read DMARC Policies ExplainedWhat a DMARC record actually controls, what none, quarantine and reject each do, and how to roll a policy out without breaking legitimate mail.6 min read Why Email Spoofing Still Works Without SPF and DMARCWhy the openness of the original email protocol makes forgery possible by default, and exactly what each authentication check does and does not stop.6 min read SPF, DKIM and DMARC: How the Three Actually Fit TogetherThree separate email authentication mechanisms that only work as a system, and why checking just one of them tells an incomplete story.6 min read Content Security Policy ExplainedWhat a CSP header actually restricts, why it matters even on a site with no obvious vulnerabilities, and how to read one without getting lost in the syntax.6 min read HSTS Explained: What It Protects and What It Does NotWhy telling a browser to always use HTTPS closes a gap a valid certificate alone leaves open, and what to check before turning it on.5 min read Reading HTTP Response HeadersWhat the headers a server sends back with every response actually mean, beyond the security specific ones, and what they can tell you about how a site is built.6 min read How HTTP Redirects Work, and Why the Chain MattersThe difference between the common redirect status codes, why a long redirect chain is a real cost, and how to check one properly.5 min read JSON Syntax Explained: What Makes JSON Valid or InvalidThe small set of rules that decide whether JSON parses correctly, and the mistakes that most often break it.5 min read JSON Versus JavaScript Objects: Why JSON Is StricterJSON looks almost identical to a JavaScript object literal, but the two are not interchangeable. Here is exactly where they diverge.5 min read Minified Versus Formatted JSON: When to Use EachWhy the same data is sometimes spread across many readable lines and sometimes squeezed onto one, and which one actually matters for what.4 min read What Base64 Encoding Actually DoesWhy Base64 exists, how it turns binary data into plain text, and why it is not, and was never meant to be, a form of encryption.5 min read Where Base64 Shows Up in Everyday DevelopmentThe places Base64 encoding turns up without anyone necessarily noticing, from image files embedded in a page to tokens passed around by an API.5 min read Base64 and File Size: Why Encoded Data Is Always BiggerThe exact reason Base64 encoded data takes up more space than the original, and when that overhead is worth accepting.4 min read Unix Time Explained: Why Computers Count from 1970What a Unix timestamp actually represents, why the count starts where it does, and why so much software relies on it instead of a calendar date directly.5 min read The Year 2038 Problem, and Whether It Still MattersWhy a number designed decades ago is set to overflow in 2038, which systems were actually affected, and how much has already been fixed.5 min read Timezones, UTC and Unix Time: Why the Same Number Looks Different EverywhereWhy a Unix timestamp has no timezone of its own, and how the same underlying moment ends up displayed differently depending on where you are.5 min read WHOIS and RDAP Explained: What Domain Registration Data Is PublicWhat a domain lookup actually reveals about who registered it, why so much of that detail is redacted today, and RDAP's role as the modern replacement for WHOIS.5 min read What Reverse DNS Is, and Why Mail Servers Check ItForward DNS turns a name into an address. Reverse DNS does the opposite, and a missing or mismatched PTR record is one of the more common reasons legitimate mail gets flagged as spam.5 min read How IP Lookup, ASN and Geolocation Data Actually WorksWhat an autonomous system is, why an IP's location is only ever approximate, and what an IP or ASN lookup can honestly tell you about an address.6 min read IPv4 vs IPv6, and Why Some Sites Still Are Not Reachable Over ItThe practical difference between the two addressing systems, why IPv6 adoption is still incomplete after more than two decades, and how to check whether a domain supports it.5 min read How to Tell What a Website Is Built WithThe headers, markup patterns and script sources that reveal a site's CMS, framework, CDN and analytics setup, and how reliable each signal actually is.6 min read