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.
Are Online Random Pickers Fair? How Randomness Works
Where a browser gets random numbers, how modulo bias and naive shuffles skew results, why streaks are normal, and what lottery odds look like.
HEX, RGB, HSL and OKLCH: Choosing a Colour Format
What HEX, RGB, HSL and OKLCH store, why HSL lightness is not perceived lightness, when OKLCH helps, and why screen colour is not print colour.
Unit Conversion Traps: Gallons, Tons and Degrees
Units that share a name but not a size, why temperature differences convert differently, area and volume, fuel economy and false precision.
Counting Days: Date Math That Trips People Up
Inclusive versus exclusive counts, adding a month to 31 January, leap years, 29 February birthdays, business days and days that are not 24 hours.
Why PDFs Get Big and How to Shrink Them
What takes up space in a PDF, how resolution and JPEG quality change the size, what merging removes, and how to keep a scan small but readable.
Sleep Cycles: When to Go to Bed and When to Wake
How sleep cycles work, how much sleep adults need, how to work out a bedtime from your alarm, and why the 90-minute rule is approximate.
Cups, Spoons and Ovens: Converting Recipes
Why a cup is not the same everywhere, why flour should be weighed, how to convert oven temperatures, and how to scale a recipe to another tin.
Percentage Mistakes: Discounts, VAT and Margins
Why two discounts do not add up, why a 50% fall needs a 100% rise, how to take VAT out of a price, and margin versus markup.
What BMI, BMR and TDEE Can and Cannot Tell You
How BMI, BMR and daily calorie needs are calculated, why one BMI means different things in different bodies, and how far to trust a calorie target.
How Interest Works: Compounding, APR and Loans
Compound versus simple interest, the rule of 72, effective rate and APR, and why a loan's early payments are mostly interest, with real numbers.
How to Check a Keyboard, Mouse and Monitor
What to test on a new or second-hand keyboard, mouse and monitor before the return window closes: dead keys, ghosting, double clicks and dead pixels.
Why numbers change when they pass through a program
0.1 plus 0.2 comes out as 0.30000000000000004, a long ID loses its last digits, and a total is a cent off. Almost all of it comes from one design decision: numbers are stored as binary fractions with a fixed budget of bits.
Why your text turns into strange characters
A name comes out as é, a Korean file becomes a wall of nonsense, or every accent is a black diamond. Text is stored as bytes and an encoding is only an agreement about what those bytes mean, so the damage tells you exactly which agreement was broken.
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.