Short, practical explanations of the formats and concepts you hit every day — each one links straight to a free tool so you can try it as you read.
A practical guide to JSON for developers — syntax rules, how to format and validate it, the most common parse errors, and how to fix them fast.
Understand JSON Web Tokens — the header/payload/signature structure, standard claims, expiry, and the security mistakes to avoid when verifying them.
What Base64 actually does, why it makes data ~33% larger, the difference between standard and URL-safe Base64, and common encode/decode gotchas.
A no-nonsense intro to regular expressions — character classes, quantifiers, anchors, groups, and the patterns you reach for most, with a tester to try them.
What a UUID is, how the common versions differ (v1, v4, v7), collision odds, and how to pick the right one for database keys and distributed systems.
What a hash function is, the difference between MD5/SHA-1/SHA-256, why fast hashes are wrong for passwords, and what to use instead (bcrypt).
Understand cron syntax — the five fields, special characters, and copy-paste schedules for every-minute, hourly, daily, and weekly jobs.
What a Unix timestamp is, why it counts from 1970, the seconds-vs-milliseconds bug that bites everyone, UTC, and the year-2038 problem.
What URL (percent) encoding does, which characters must be escaped, the difference between encodeURI and encodeURIComponent, and common gotchas.
A clear explanation of CSS color formats — HEX, RGB/RGBA, and HSL — how they map to each other, alpha transparency, and which to reach for.
A practical Markdown reference — headings, emphasis, lists, links, code, and tables — plus the flavor differences (CommonMark vs GitHub Flavored Markdown).
What actually makes a password strong — entropy and length over clever substitutions — plus passphrases, reuse, and how passwords should be stored.
How number bases work and why programmers use binary and hexadecimal — with the mental model for converting between base 2, 8, 10, and 16.
What HTML entities are, the characters you must escape, named vs numeric references, and why escaping is your first line of defense against XSS.