Developer Learning Guides
Practical guides on regex, CSS, JSON, and more — with interactive examples.
Regex Basics: A Complete Beginner's Guide
Learn regular expressions from scratch. Understand patterns, metacharacters, and how to write your first regex.
Regex Special Characters: Complete Reference
Master every regex metacharacter and special character with examples and interactive tests.
Regex Groups and Captures Explained
Learn how to use capturing groups, non-capturing groups, and named groups to extract data with regex.
Regex Quantifiers: Complete Guide
Master greedy, lazy, and possessive quantifiers in regular expressions with practical examples.
CSS Selectors: The Complete Guide
Learn every type of CSS selector — from basic to advanced — with examples and specificity explanations.
CSS Specificity: Why Your Styles Aren't Applying
Understand how CSS specificity works, how to calculate it, and how to avoid the !important trap.
JSONPath Syntax: Query JSON Like XPath
Learn JSONPath syntax to query, filter, and extract data from nested JSON structures.
Unix Timestamps Explained
Everything you need to know about Unix time — what it is, how it works, and common pitfalls.
Base64 Encoding Explained
Understand what Base64 is, how it works, when to use it, and when not to.
JWT Structure and How It Works
Understand JSON Web Tokens: their structure, how to decode them, and when to use (and not use) them.
JWT vs Session Tokens: Which Should You Use?
Understand the fundamental differences between stateless JWT authentication and stateful session tokens, with concrete guidance on which fits your use case.
JWT Refresh Tokens Explained
Learn how refresh tokens extend JWT authentication sessions securely, without requiring users to log in again every 15 minutes.
Hash Functions Explained: MD5, SHA-256, and When to Use Each
Learn what hash functions do, why cryptographic hashes are one-way, and which algorithm to use for passwords, checksums, and data integrity.
URL Encoding Explained: What %20 Actually Means
Understand percent-encoding, why spaces become %20, when to use encodeURI vs encodeURIComponent, and how to decode URLs correctly.
JSON Schema Explained: Validate Your JSON Data
Learn how JSON Schema works, how to write validation rules for objects and arrays, and how to use it for API request validation and OpenAPI documentation.
JSON vs YAML: Which Should You Use?
Compare JSON and YAML for configuration files, API responses, and data interchange — with concrete rules for when each format is the right choice.
JSON.stringify and JSON.parse: Edge Cases You Should Know
Master JavaScript JSON serialization — what stringify drops, how to handle dates and undefined, the replacer and reviver functions, and circular reference errors.
Regex Lookahead and Lookbehind: Match Without Consuming
Understand zero-width assertions in regex — how lookahead and lookbehind let you match based on surrounding context without including that context in the result.
Regex for Email Validation: The Right Approach
Learn why perfect email regex is impossible, what a practical validation pattern looks like, and when to use client-side vs server-side validation.
The CSS Box Model: margin, padding, border, and content
Understand how every HTML element is rendered as a rectangular box, how margin and padding differ, and how box-sizing:border-box changes layout forever.
Flexbox vs CSS Grid: When to Use Each
Learn the fundamental difference between one-dimensional Flexbox and two-dimensional Grid, with practical examples for navbars, galleries, and page layouts.
CSS Custom Properties (Variables) Explained
Learn how CSS custom properties work, how they differ from preprocessor variables, and how to use them for theming, dark mode, and dynamic styling.
ISO 8601 Explained: The Right Way to Format Dates
Learn the ISO 8601 date and datetime standard, why 2026-06-13T10:30:00Z is unambiguous, and how to use it correctly in APIs and databases.
Unix Timestamps vs ISO 8601: Which to Use in Your API?
Compare Unix epoch timestamps with ISO 8601 strings for API design, database storage, and JavaScript date handling — with a clear recommendation.
UTF-8 Explained: How Computers Store Text
Understand how UTF-8 encodes every writing system into bytes, why it became the universal standard, and how encoding bugs appear in real applications.
CORS Explained: Why Your API Call is Blocked
Understand why browsers enforce the Same-Origin Policy, how CORS headers unlock cross-origin requests, and how to configure CORS correctly on your server.
HTTP Status Codes: A Practical Developer Guide
Learn what each HTTP status code range means, which codes to use in your REST API, and how to avoid the most common status code mistakes.
Named Capture Groups in Regex: Clean Extractions
Learn how named capture groups make regex results readable, how to access them in JavaScript, and why they beat numbered groups for complex patterns.
Color Spaces Explained: RGB, HSL, HEX, and Beyond
Understand how computers represent color. Learn the differences between RGB, HSL, HEX, HSV, and OKLCH — and when to use each one.
Color Contrast for Developers: WCAG Rules and How to Check
Learn the WCAG contrast requirements for text, icons, and interactive elements — and how to test contrast ratios in your projects.
Number Bases Explained: Binary, Octal, Decimal, and Hex
Understand how number systems work — from binary and octal to decimal and hexadecimal — with practical examples for developers.
Bitwise Operations for Web Developers
A practical guide to AND, OR, XOR, NOT, and bit shifting — with real use cases like feature flags, permissions, and colour manipulation.
HTML Semantic Elements: A Complete Reference
Learn which HTML elements to use for headers, navigation, articles, sections, and more — and why semantics matter for SEO and accessibility.
Text Encoding for Developers: ASCII, UTF-8, and Unicode
How computers store text — from ASCII to Unicode to UTF-8. Understand encoding errors, BOM, and why mojibake happens.
What is Regex? Complete Guide for Developers
Master regular expressions from patterns and flags to groups, lookahead, named captures, and common mistakes across JavaScript, Python, and other languages.
JSON Format Explained: Structure, Syntax, and Common Errors
Understand JSON syntax, valid vs invalid values, parsing in JavaScript and other languages, the difference from JSON5, and how to validate JSON with schemas.
How JWT Works: Header, Payload, Signature Decoded
Understand JWT structure, how HS256 and RS256 signing work, when to use JWT over sessions, and the security mistakes that get apps breached.
How to Convert Any Website to Markdown (for LLMs, RAG & Docs)
Compare every way to turn a web page into Markdown — pandoc, Turndown, browser tools, and hosted crawlers — and learn when each one breaks down.
Preparing Website Content for RAG: Clean Markdown Pipelines
Why clean Markdown beats raw HTML for RAG, how to strip boilerplate and crawl sitemaps, and how to build the pipeline with or without your own infrastructure.