Guides
The tools answer a question quickly. These explain the thing behind the question - why random primary keys slow down inserts, why two contrast checkers disagree, why a string that looks identical to another one compares unequal.
Each is written for someone mid-debug rather than someone browsing, so they lead with the mechanism and the failure mode rather than with definitions. Every guide links to the tools that apply it.
UUID v7 vs v4: why time-ordered keys index better
Random keys scatter B-tree inserts across the index. Time-ordered keys append. The difference is measurable, and v7 gets it back without giving up offline generation.
APCA vs WCAG 2.1: why two contrast checkers disagree
One is a symmetric luminance ratio, the other models perception and is signed by polarity. They disagree most exactly where dark mode lives.
Invisible Unicode: zero-width characters and homoglyph attacks
Trojan Source, lookalike package names and identifiers that compare unequal while rendering identically. All invisible in an editor.
Seconds or milliseconds? Reading Unix timestamps correctly
Nothing in the number states its unit. Digit count is the tell, and getting it wrong is the most common date bug in any codebase.
Why OKLCH produces better palettes than HSL
A yellow and a blue at the same HSL lightness look nothing alike. That single fact explains most bad generated palettes.
Decoding a JWT is not verifying it
The payload is readable by anyone. Treating a decoded claim as authenticated is the vulnerability, and it is common.
MD5, SHA-1, SHA-256: what each is still safe for
Broken against a deliberate attacker is not the same as useless. The question is always who you are defending against.
Reading and writing cron expressions
Terse to the point of being write-only, with two genuinely surprising behaviours that bite almost everyone once.
Base64 is not encryption
A transport encoding that gets mistaken for a security measure roughly once per code review.
JSON, YAML, TOML or CSV: choosing a config format
Four formats, four different sets of sharp edges. Picking deliberately saves an afternoon later.