Guides

In-depth, original articles on how the tools work and the ideas behind them — from barcode check digits to number bases, encodings and browser privacy.

• Why your QR code won't scan on some phones

  It works on your desk and fails on the poster. QR codes are read by finding three corner squares in a clean margin, and most scanning failures are a margin, a contrast or a size problem rather than anything wrong with the data inside.

• Why your PDF isn't searchable

  You can read every word on the page, but the search box finds nothing and selecting text selects a picture. A PDF page is a set of drawing instructions, and a scanned page draws one photograph — the letters you see were never stored as letters.

• Why your photos rotate when you upload them

  A photo looks upright on your phone, then lands sideways on the website you uploaded it to. The pixels never moved: the camera stored the picture the way the sensor read it and attached a note saying which way is up, and not every program reads that note.

• Why your MP3 tags look different in every player

  One player shows the old album name, another shows the new one, and the artwork only appears on your phone. The file usually carries two sets of tags, and players disagree about which to believe.

• Why Excel breaks your CSV, and how to stop it

  Leading zeros vanish, long order numbers lose their last digit, and product codes turn into dates. None of it is a bug: it is Excel guessing a type for every field as it opens the file.

• Unicode Normalization and Invisible Characters

  Why two identical-looking strings can fail an equality check, what NFC, NFD, NFKC and NFKD actually do, which invisible characters hide in pasted text, and the rules that keep text handling safe.

• IP Addresses and Subnets, Without the Hand-Waving

  What an IP address really is, how to read CIDR notation and count the hosts in a prefix, which ranges must never be routed, how IPv6 changes the arithmetic, and why sorting addresses as text goes wrong.

• How Cron Schedules Actually Work

  The five cron fields and their syntax, the day-of-month/day-of-week rule almost everyone gets wrong, what daylight saving does to a nightly job, and how to design schedules that survive restarts.

• Regular Expressions in Practice

  How a regex engine actually scans a string, why anchors and greediness change everything, what catastrophic backtracking is, and the formats you should never try to parse with a pattern.

• Colour Contrast and Accessible Palettes

  What the WCAG contrast ratios actually measure, why a colour that looks fine can still fail, how colour blindness changes the picture, and how to build a palette that holds up.

• Working with CSV Files Without Breaking Them

  Why CSV keeps going wrong — quoting, delimiters, encodings, leading zeros and dates — and how to move data between spreadsheets, JSON and SQL without silent corruption.

• Passwords and Passphrases: What Actually Makes One Strong

  Why length beats symbol substitution, where password strength meters mislead, how passphrases work, and what two-factor authentication does and does not protect.

• Compressing and Resizing Images for the Web

  How to make images small without making them look bad: resize before you compress, pick the right format, and understand what a quality slider actually does.

• Working with Time Zones and Unix Timestamps Without Bugs

  Why time is so hard to get right in software — UTC, Unix timestamps, time zones and DST — and a small set of rules that prevent the most common date-handling bugs.

• Choosing an ID Format: UUID, ULID, Snowflake or Auto-increment

  A practical guide to picking identifiers — auto-increment integers, UUID v4/v7, ULID and Snowflake IDs — and the trade-offs in uniqueness, ordering, size and privacy.

• Hashing vs Encryption vs Encoding: What's the Difference

  Three terms that are constantly confused — hashing, encryption and encoding — explained clearly, with what each is for, when to use which, and the mistakes to avoid.

• Number Bases and Text Encodings: A Developer's Cheat Sheet

  A practical primer on binary, octal, decimal and hexadecimal, plus how text becomes bytes through UTF-8, Base64 and URL encoding — with the rules you actually need.

• Why In-Browser Tools Keep Your Data Private

  How client-side tools work, why running entirely in your browser means your data never leaves your device, and how to verify that claim yourself.

• How Barcode Check Digits Work (EAN-13, UPC-A, EAN-8)

  A clear, practical explanation of the GS1 modulo-10 check digit on retail barcodes — how it is calculated, why it catches errors, and how to validate a code by hand.