Test Credit Card Numbers: How the Luhn Check and Card Prefixes Work
How card numbers are structured (IIN, length, Luhn check digit), how to test payment forms safely and when to use your gateway’s official test cards.
Category: Developer & Security
How to Create Strong Passwords You Don’t Have to Remember
What makes a password strong in 2026, how long it should be, why random beats clever, and how to generate and store secure passwords the easy way.
What Is a UUID? Version 4 Explained for Developers
How UUIDs and GUIDs work, what version 4 means, collision odds, database key trade-offs and formatting options — with a bulk UUID v4 generator.
Random IP Addresses for Testing: Public, Private, IPv4 & IPv6
IPv4 vs IPv6, public vs private ranges, reserved blocks to avoid and how to generate realistic IP addresses for logs, firewalls and network demos.
MAC Addresses Explained: Formats, OUIs and Locally Administered Bits
How MAC addresses are built, what the locally administered and multicast bits mean, and how to generate safe random MACs for VMs and network testing.
IMEI Numbers Explained: Structure, TAC and Check Digit
What the 15 digits of an IMEI mean, how the Luhn check digit validates it, and how to generate valid-format IMEIs for MDM and telecom software testing.
API Key Best Practices: Generate, Store and Rotate
API key best practices for developers: how long a secret should be, which alphabet to use, how to store keys safely and rotate them without downtime.
How to Choose a Secure PIN Code (and Remember It)
How to choose a secure PIN code for your phone, bank card or alarm: patterns to avoid, why length matters, and simple tricks to remember a random PIN.
Diceware Passphrases Explained: Why Words Beat Symbols
Diceware passphrases explained: how random words create strong, memorable passwords, how word lists turn into bits of entropy, and how many words you need.
Localhost Ports Explained: Picking One for Dev Servers
Localhost ports explained: what port numbers mean, which ranges are safe for dev servers and containers, and how to fix “address already in use”.
How to Read a User Agent String, Token by Token
Learn how to read a user agent string: what Mozilla/5.0, AppleWebKit and KHTML mean, why every browser claims to be Safari, and how to test UA parsing.
How to Choose a Domain Name: A Practical Checklist
How to choose a domain name for a startup, blog or side project: a checklist on length, spelling, extensions and brand checks before you register.
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