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UUID v4 Breaks Database Performance at Scale — What UUID v7 Changed and Why It's Still Not the Default
Design Tokens, CSS Variables, and Dark Mode: How to Build a Colour System That Scales
Design tokens are a three-tier hierarchy: primitive colours → semantic meanings → component-specific use. CSS custom properties implement this at runtime, making dark mode a one-place change. Here's the full token model, how Tailwind's colour system works, and why OKLCH is replacing HSL for design systems.
How Email Attachments Work: MIME Encoding, Base64, and Why Binary Files Need Encoding
Email attachments work because MIME uses Base64 to encode binary files as ASCII text — a system designed in 1992 when email could only carry 7-bit ASCII. Here's how MIME multipart email works, why binary needs encoding, the 33% Base64 overhead on attachment sizes, and how the same system handles HTML form file uploads.
Production Scheduled Jobs: Idempotency, Monitoring, and Modern Alternatives to Cron
Cron jobs fail silently and traditional cron has no alerting, no history, and no overlap prevention. Here's idempotency design for scheduled jobs, modern alternatives (Celery Beat, AWS EventBridge, Kubernetes CronJobs), and the dead man's switch monitoring pattern.
JSON Schema Validation and API Contracts: OpenAPI, Contract Testing, and Validation Libraries
JSON Schema validates structure and constraints — and OpenAPI uses it as the contract format for API documentation, client SDK generation, and contract testing. Here's how JSON Schema works, key validation keywords, how OpenAPI extends it, and how Pact implements consumer-driven contract testing.
JSON Parsing in Python, JavaScript, Go, and Ruby: Edge Cases That Cause Real Bugs
Python's None vs JSON null, JavaScript's integer precision limit at 2^53, Go's strict struct tags, and Ruby's symbolize_names security concern are real production pitfalls. Here's the JSON parsing edge cases in each major language and how they cause bugs at API boundaries.
XSS and HTML Encoding: The Five Contexts That Require Different Escaping
XSS is still the most common web vulnerability — and unescaped HTML is the mechanism. Here's how cross-site scripting actually works, the five encoding contexts that require different treatment, why React is safe by default but PHP isn't, and how CSP adds a second layer.
HTTP Status Codes Explained: A Complete Debugging Guide for API Work
HTTP status codes have precise meanings that most developers only half-know. Here's the complete guide — every important 2xx, 3xx, 4xx, and 5xx code explained with debugging guidance for each.
JWT Security Vulnerabilities: alg:none, Algorithm Confusion, and Secure Token Storage
The alg:none attack, RS256/HS256 algorithm confusion, weak HS256 secrets, localStorage vs httpOnly cookies, and revocation without statefulness — JWT security vulnerabilities are specific and avoidable. Here's how each one works and how to fix it.
Secure Randomness: Why Math.random() Fails for Security Tokens — and the Right Alternatives
Math.random() in JavaScript is predictable from 128 observations. Python's random module explicitly warns it's not for security. Here's why PRNGs fail for tokens, the secure alternatives in every major language, and the specific bit lengths needed for different security contexts.
API Authentication Methods Compared: Keys, Bearer Tokens, OAuth 2.0, and HMAC
API keys, Bearer tokens, Basic Auth, OAuth 2.0, and HMAC signatures each fit different authentication scenarios. Here's how each method works, when it's the right choice, and how to test each one in an API checker — with the specific header formats.
Bit Manipulation and Bitmasks: From Unix Permissions to Feature Flags
Bit manipulation is where number bases become practical: Unix permissions, feature flags, IP subnetting, and protocol fields all use bitmasks. Here's how AND, OR, XOR, and shifts work, with real examples from file permissions and flag systems.
Merkle Trees and Hash Functions: How Git, Blockchain, and Certificate Transparency Work
Hash functions underpin Git commits, blockchain blocks, and certificate transparency logs through Merkle trees. Here's why MD5 and SHA-1 are "broken," how Merkle trees verify large datasets with O(log n) hashes, and how Bitcoin light clients verify transactions without the full blockchain.
