Reference Tables
Comprehensive lookup tables for the technical data developers actually need at hand: ASCII codes, HTTP MIME types, HTTP headers, HTML entities. Each page is a single dense reference — bookmark-friendly, printable, factually accurate.
Stripe Test Card Numbers — Every Card + What They Trigger (2026)
Every Stripe test card number for successful charges, declines, 3D Secure, disputes, and fraud. Card, CVC, ZIP, and what the API returns. No signup, single page reference.
Cron Syntax Reference — Every Field, Every Shortcut, Every Gotcha
Complete crontab reference: the 5 fields, ranges, steps, @reboot / @daily shortcuts, weekday/dayofmonth OR gotcha, timezone handling, and 30 real cron examples.
Unicode Symbols Reference — Copy Common Characters (Arrows, Math, Emoji, Currency)
Copy-paste common Unicode characters — arrows, math symbols, currency, em/en dashes, smart quotes, box drawing, and emoji. With code point, HTML entity, and JS escape for each.
CSS Specificity Explained: The 4-Tuple, !important, and @layer
How CSS specificity actually works: the 4-tuple scoring system, :where/:is/:not quirks, !important pitfalls, and using @layer to end specificity wars.
JavaScript Closures Explained: Scope, Patterns, and Pitfalls
Understand JavaScript closures with practical examples: private state counters, module pattern, currying, memoization, and the classic var loop bug fix.
JavaScript this Keyword Explained: 4 Binding Rules & Arrow Functions
Master JavaScript's this keyword with the 4 binding rules in resolution order, arrow function behavior, and fixes for common callback and setTimeout bugs.
ASCII Table — Complete Reference (Decimal, Hex, Binary, Octal)
Complete ASCII character table with decimal, hexadecimal, binary, and octal codes for all 128 standard ASCII characters. Free, printable, no signup.
HTTP MIME Types Reference — Complete List by Category
Complete reference of HTTP MIME types (Content-Type headers): application, text, image, audio, video, multipart. With file extensions and use notes.
HTTP Headers Reference — Complete List with Examples
Reference for all common HTTP headers: request, response, security, caching, CORS, content negotiation. With practical examples and modern best practices.
HTML Entities Reference — Complete List of Special Characters
Complete HTML entity reference for special characters, symbols, math, currency, arrows, Greek letters, and more. With named, decimal, and hex codes.
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