Guides & Tutorials
Practical, privacy-first developer guides — using free tools that run entirely in your browser.
What Online Tools Do With Your Data: We Measured 28
We drove 28 popular online tools with a marked payload and recorded every request: paste-based tools uploaded it 2 times in 15, file-based ones 3 in 5.
How AI Text Detectors Work: Methods, Accuracy, and Limitations
AI text detectors use burstiness, perplexity, and phrase patterns to estimate whether text was AI-generated, but none is definitive. Here's how they work.
How to Calculate Your Freelance Rate (The Complete Formula)
Copying other freelancers' rates leads to underpricing. A formula that accounts for taxes, expenses, and non-billable hours, and why it comes out higher.
The True Cost of Your Meetings (And How to Reduce It)
A 1-hour meeting with 8 engineers costs more than most people realize. How to calculate a meeting's cost and ROI, and when to go async instead.
Heart Rate Training Zones Explained: From Fat Burn to VO2 Max
The 5 heart rate training zones explained: the Karvonen formula, what happens in each zone, and how to build a weekly training plan around them.
JSON Schema, Joi, Mongoose, and Zod: Which Validator Should You Use?
Joi, Zod, Mongoose schemas, or JSON Schema? When each validation approach fits best, with code examples for the most common patterns.
OpenAPI to TypeScript: Auto-Generate Types from Your API Spec
Stop writing API types by hand. Learn how to generate TypeScript interfaces directly from OpenAPI 3.0 specs — and keep them in sync automatically.
Schema.org Markup: The Complete Guide to Rich Results in 2026
How structured data can earn rich results in Google Search, such as product ratings and recipe cards, and how to implement the major schema types.
Regular Expressions Explained: From Basics to Advanced Patterns
Regex intimidates most developers, but it doesn't have to. This guide breaks down every major pattern with practical examples you'll actually use.
CSS Color Systems: HSL, oklch, and Building a Design Token Palette
Beyond hex codes: how HSL, oklch, and design tokens work together to build a CSS color system that is easy to maintain.
10 Financial Calculations Every Developer Should Know How to Build
The math behind the personal finance calculators that matter most, from compound interest to mortgage amortization.
Debt Snowball vs Avalanche: The Math and Psychology of Paying Off Debt
The snowball method feels good; the avalanche saves the most money. The math on both, and why the one that works is the one you'll stick with.
Blood Pressure Numbers Explained: What Systolic, Diastolic, and MAP Really Mean
What the two numbers of a blood pressure reading mean, the stages of hypertension, and evidence-based ways to lower yours.
Heart Rate Zones, FTP, and 1RM: The Fitness Metrics That Actually Matter
Beyond step counts: heart rate training zones, functional threshold power for cyclists, and strength percentages for weightlifters.
Git Branch Naming, Commit Messages, and Workflow Conventions That Scale
Good Git hygiene is invisible when it works and painful when it doesn't. What matters in branch naming, commit conventions, and team workflow.
README, CONTRIBUTING, and License: The Open Source Documentation Checklist
A project without good documentation is invisible. Every file your open source project needs, from the first README to the CONTRIBUTING guide.
Email Subject Lines That Get Opened: Data, Psychology, and Common Mistakes
Your subject line decides whether an email is opened or ignored. What the research says about its length, power words, personalization, and spam filters.
Prisma, Drizzle, TypeORM, Mongoose: Choosing the Right ORM for Your Stack
ORMs abstract database access, but each trades off type safety, performance, and developer experience differently. How to choose between the major ones.
JSON, YAML, TOML, HCL, and When to Use Each Configuration Format
A practical comparison of JSON, YAML, TOML, and HCL for config files — when each shines and where each fails.
Core Web Vitals in 2026: LCP, INP, CLS and How to Actually Fix Them
What each Core Web Vital measures — LCP, INP, and CLS — what commonly makes a page fail it, and the most effective fixes for each.
Freelance Developer Finances: Rates, Invoices, Taxes, and the Numbers You Need to Know
The math of sustainable freelance pricing — taxes, non-billable time, and client-facing rates — and why a rate set once needs revisiting.
Complex Numbers Explained: From i to Fourier Transforms
Complex numbers, used in signal processing, quantum mechanics, and electrical engineering, explained from basic arithmetic to polar form.
Descriptive Statistics Every Developer Should Know: Mean, Median, Regression, and More
The descriptive statistics that come up in real data analysis work, for developers who learn statistics on the job.
Character Limits, Hashtags, and Algorithms: A Developer's Guide to Social Media Content
The character limits, image sizes, and optimization tips that matter on each major social media platform.
The 50/30/20 Budget Rule: How to Actually Build a Budget That Sticks
Budgets fail when they are too complicated or too strict. The 50/30/20 rule is simple to follow and structured enough to make progress on savings and debt.
Terraform HCL Explained: Blocks, Arguments, Expressions, and Common Patterns
HCL, the HashiCorp Configuration Language of Terraform, explained: its syntax, block types, expressions, and the patterns you'll use in every project.
CSS Flexbox: The Complete Guide to Flexible Layouts
Master CSS Flexbox — flex-direction, justify-content, align-items, flex-grow, gap — with real layout examples for nav bars, card grids, and centering.
CSS Grid: The Complete Guide to Two-Dimensional Layouts
Learn CSS Grid from scratch — grid-template-columns, fr units, auto-fill, minmax, named areas — with examples for holy grail, magazine, and card layouts.
CSS Animations and Transitions: A Practical Guide
Smooth hover effects and keyframe animations in CSS — transitions, @keyframes, GPU-accelerated properties for performance, and prefers-reduced-motion.
Dates and Timestamps in JavaScript: A Developer's Guide
Avoid common Date pitfalls — Unix timestamps, Intl.DateTimeFormat, IANA timezones, ISO 8601, and the hidden UTC vs local parsing trap in new Date().
How QR Codes Work and How to Generate Them Online
Understand QR code structure — finder patterns, error correction levels, encoding modes — and best practices for URLs, WiFi, and vCard generation.
Cron Expressions Explained: Syntax, Examples, and Tips
Decode the 5-field cron syntax — minute, hour, day, month, weekday — with annotated examples of common schedules, special characters, and GitHub Actions.
HTTP Status Codes: A Developer's Complete Reference
Every HTTP status code class explained with REST API design guidance — when to use 201 vs 200, 401 vs 403, 301 vs 302, and common mistakes to avoid.
Markdown Syntax Guide: Formatting from Basics to Advanced
A complete Markdown reference — headings, bold, links, images, tables, fenced code blocks, task lists, and GFM vs CommonMark differences.
SEO Meta Tags Explained: Title, Description, and Open Graph
Write title tags, meta descriptions, canonical links, and Open Graph tags that help rankings and social sharing — with optimal lengths and common mistakes.
CSS Units Explained: px, rem, em, vw, vh, and When to Use Each
Know when to use px, rem, em, vw, vh — including the em compounding trap, rem for accessibility, svh/dvh for mobile, and fluid typography with clamp().
Encryption vs Hashing: What's the Difference and When to Use Each
Encryption is reversible; hashing is not — understand when to use each, why MD5/SHA-1 fail for passwords, how salting works, and what HMAC adds.
Image Formats for the Web: JPEG, PNG, WebP, and SVG Compared
When to use JPEG, PNG, WebP, SVG, or AVIF — with a decision guide, the Core Web Vitals impact of each, and picture element fallback patterns.
CAGR Explained: What It Is, the Formula, and How to Use It
What Compound Annual Growth Rate is, how to calculate it from start/end values and years, why it differs from average return, and when to use CAGR vs IRR.
SPF, DKIM, and DMARC Explained: Email Authentication for Developers
How SPF, DKIM, and DMARC work together to prove email is legitimate and stop spoofing — with record syntax, common mistakes, and a step-by-step setup.
Mbps vs MB/s: Network Speed Units Explained
1 MB/s = 8 Mbps, so a 100 Mbps plan downloads at most 12.5 MB/s, about 11.8 once TCP runs over Ethernet. Bits vs bytes, binary units and transfer times.
Runtime Type Validation with Zod: A Practical Guide
Why TypeScript types aren't enough at runtime, how Zod validates API responses and environment variables, and how to generate a Zod schema from JSON.
Classic Ciphers Explained: Caesar, Atbash, Vigenère, and Polybius
How classic substitution ciphers work — Caesar, Atbash, Vigenère, and the Polybius square — with the math behind each and why they're insecure today.
HTTP Security Headers Explained: CSP, Cookies, and Robots
The HTTP security headers every web app should set — Content-Security-Policy, Set-Cookie flags, X-Robots-Tag, and CORS — with a generator for each.
IP Addressing Explained: Decimal, Binary, Hex, and Subnets
How IP addresses work in dotted decimal, binary octets, and hexadecimal — plus CIDR subnet masks, private ranges, and loopback addresses, explained simply.
Fraction Arithmetic: Add, Subtract, Multiply, and Divide Step by Step
How to add, subtract, multiply, and divide fractions — the lowest common denominator, simplifying with the GCD, and mixed numbers — with worked examples.
CSS Resets vs Normalize: Which Reset Should You Use in 2026?
CSS resets compared — Eric Meyer's Reset, Normalize.css, a modern minimal reset, and Tailwind Preflight: when to use each, and what each changes.
CSS Gradients: Linear, Radial, and Conic — A Complete Guide
Master CSS gradients — linear, radial, and conic — with syntax breakdowns, multi-stop techniques, animation tips, and a free in-browser gradient generator.
JavaScript Regex Flags Explained: g, i, m, s, u, y, d
A practical guide to all seven JavaScript regex flags — what each does, when to use it, and common gotchas — with live examples you can run in a browser.
Password vs Passphrase: Entropy, Memorability, and Security in 2026
Why passphrases can be stronger and far easier to remember than complex passwords — the entropy math behind it, and how to generate both securely.
CSS Clamp for Responsive Typography: No Media Queries Needed
How CSS clamp() replaces brittle media-query font stacks with one rule that scales smoothly between two viewport sizes — with a calculator and examples.
CSS Custom Properties: A Practical Guide to Design Tokens
What CSS custom properties (CSS variables) are, how to structure a design token system with them, and how to generate a full color scale.
Regular Expressions Quick Reference: Common Patterns Explained
The most useful regex patterns for developers — email, URL, date, number, word boundaries — explained with examples and a free in-browser tester.
JSON to Go, Rust, TypeScript: Code Generation Tools for Any Language
Stop writing boilerplate struct definitions by hand — paste a JSON sample and generate typed structs for Go, Rust, TypeScript, and PHP in your browser.
What to Put in .gitignore (and Why)
Which files and directories to keep out of version control for Node, Python, Go, Rust, and more — plus the .gitignore pattern syntax worth knowing.
How to Merge, Split, and Rotate PDFs in Your Browser (No Upload Required)
Edit PDFs entirely client-side with pdf-lib — merge, split by page range, rotate and remove pages, and convert images to PDF without uploading a file.
Designing for Color Blindness: What Every Developer Should Know
The four main types of color vision deficiency, how they affect your UI, and the steps that make a web app accessible — with tools to simulate and test.
Generating Fake Test Data for Development and QA
How to create realistic fake names, emails, addresses, and IDs for unit tests, database seeding, UI demos, and privacy-safe sharing, without external APIs.
Generating JSON Schema from Example Data: A Practical Guide
How JSON Schema works, how to generate one from an existing JSON document, and how to use it for API validation, TypeScript generation, and documentation.
Why Client-Side Tools Are Safer: Free, Private, No Upload
Client-side tools run in your browser, so your JSON, tokens, and secrets never leave your device. Why that matters, and how to tell the difference.
Pure CSS UI: Buttons, Loaders, and Animations Without JavaScript
Build buttons, loading spinners, and keyframe animations with CSS alone — no JavaScript, no images — for lighter pages, with a free generator for each.
BMR, TDEE, and Body Fat: The Numbers Behind Your Calorie Goals
How BMR, TDEE, and body-fat percentage relate — what each number means, the formulas behind them, and how to use them to plan a cut or a bulk.
How Mortgage Payments Work: PITI, Interest, and PMI Explained
What makes up a monthly mortgage payment — principal, interest, taxes, insurance, and PMI — plus the amortization formula and how to estimate yours.
URL Encoding and Decoding, Explained
What percent-encoding is, which characters need escaping, encodeURI vs encodeURIComponent, and how to encode or decode URLs safely in your browser.
MD5 vs SHA-256: Which Hash Should You Use?
MD5, SHA-1 and SHA-256 compared — what hashing is, why MD5 and SHA-1 are broken for security, when each is still fine, and how HMAC differs.
UUID vs ULID vs Nano ID: Choosing an ID Format
How UUID, ULID and Nano ID differ in randomness, sortability, length and URL-friendliness, and which to pick for database keys, public IDs and short links.
How to Format and Validate JSON Online
Format, validate, minify, and convert JSON entirely in your browser — plus the privacy reason you shouldn't upload sensitive payloads to a server.
How to Decode a JWT Safely in Your Browser
What's inside a JWT, how decoding differs from verifying, and how to read a token's claims without sending a live credential to someone else's server.
Base64 Encoding and Decoding, Explained
What Base64 actually is, when to use it, why it is NOT encryption, the 33% size overhead, and Base64 vs Base64URL — with a free in-browser encoder/decoder.