Guides & Tutorials

In-depth guides on the problems our tools solve — formats, encodings, security, and more.

• Barcodes Explained: Code 128, EAN-13, and Beyond

  Barcodes quietly run retail, inventory, and shipping. This guide explains the difference between 1D barcodes and QR codes, the common types like Code 128 and EAN-13, and how to generate a barcode for a product or label.

  2026-09-03

• Date Math Made Easy: Days Between Dates and Adding Days

  Calculating the days between two dates, or what date falls 30 days from now, is surprisingly error-prone by hand. This guide explains how date arithmetic works — leap years, uneven months, year rollovers — and how to get the right answer instantly.

  2026-09-03

• Emoji and Special Characters: How to Find, Copy, and Use Them

  Finding the right emoji, arrow, symbol, or Greek letter is annoyingly difficult if you don't know how to search for it. This guide explains how Unicode characters work and how to find, copy, and use emoji and special symbols anywhere.

  2026-09-03

• EXIF Data Explained: What Your Photos Reveal (and Hide)

  Every photo carries hidden metadata — camera, settings, sometimes even location. This guide explains what EXIF data is, why it's useful for learning photography, and why it matters for privacy before you share an image.

  2026-09-03

• How to Compress and Resize Images: A Practical Guide

  Big images are the number one cause of slow pages. This guide explains the difference between file size and dimensions, why lossless vs. lossy matters, and how to compress or resize an image in your browser in seconds.

  2026-09-03

• How to Create a Professional Invoice (and a Certificate)

  A good invoice does two jobs: it tells the client what they're paying for and makes paying easy. This guide walks through what to include, how to calculate totals, and how to put one together without accounting software.

  2026-09-03

• MIME Types Explained: What Content-Type Really Means

  Broken images, downloads that should display, CSS that arrives as plain text — these are all MIME-type problems. This guide explains what MIME types are, how the Content-Type header works, and how to look up the right one.

  2026-09-03

• Morse Code for Beginners: How to Read and Write It

  Morse code turns letters into dots and dashes, and it used to carry messages across telegraph wires and radio. This guide teaches the basics — how the timing works, how to decode a message, and how to read the famous SOS.

  2026-09-03

• Percentage Math Made Easy: Discounts, Tax, Tips, and More

  Percentages show up everywhere — sales, taxes, tips, grades. This guide explains the three core percentage problems, how discount and tax math actually work, and how to get a clear answer without doing arithmetic in your head.

  2026-09-03

• The Pomodoro Technique: Focus in 25-Minute Bursts

  Fighting distraction? The Pomodoro Technique breaks work into focused intervals separated by breaks. This guide explains the method, why 25 minutes works, how to customize it, and how a timer keeps you honest.

  2026-09-03

• QR Codes Explained: How They Work and How to Make Your Own

  QR codes are everywhere, but most people never think about how they store data. This short guide walks through the basics of QR codes, what the error-correction levels actually do, and how to generate and scan your own in seconds.

  2026-09-03

• Randomness Explained: From Coin Flips to Secure Generators

  How random is a click of a button? This guide explains why dice rolls and coin flips feel random, how random number generators really work, and when you need cryptographically secure randomness instead of a quick shuffle.

  2026-09-03

• How to Read and Format SQL: From One-Line Mess to Clean Code

  Databases often give you tangled, single-line queries that are impossible to review. This guide explains why readable SQL matters, what a SQL formatter actually does, and how to turn a cramped query into clean, indented code.

  2026-09-03

• How to Turn Text into a PDF

  A plain text file looks different on every device, but a PDF looks the same everywhere. This guide explains why PDF is the go-to for fixed-format sharing, how to convert text to PDF without installing anything, and how to get clean pagination.

  2026-09-03

• URL Slugs: How to Turn Any Title into a Clean, SEO-Friendly Link

  A slug is the readable part of a URL, and it matters more than most people think. This guide explains what a slug is, why hyphens beat underscores, how long it should be, and how to turn any title into a URL-ready slug in one click.

  2026-09-03

• Text to Speech: How to Turn Words into Audio

  Text to speech turns written words into spoken audio, which is a lifesaver for accessibility, learning, and content creation. This guide explains how TTS works, what to use it for, and how to generate speech from text right in your browser.

  2026-09-03

• Time Differences and Due Dates: How to Calculate Them

  How many hours between now and the meeting? When is the invoice due? This guide covers the two time questions that come up constantly — elapsed time and deadlines — and how to get a clear answer without mental math.

  2026-09-03

• Units Made Simple: Converting Length, Weight, Temperature, and More

  Recipes in ounces, specs in millimeters, flight speeds in knots — unit conversion is a daily friction. This guide explains how conversion works, why temperature is the odd one out, and how to convert between metric and imperial instantly.

  2026-09-03

• What Is JSON? A Beginner's Guide to the Web's Data Format

  JSON is the language APIs, databases, and configuration files use to talk. This guide explains the six JSON types, why it beat XML, and how to format, validate, and minify JSON with confidence.

  2026-09-03

• Word Count, Reading Time, and How to Hit a Target

  Word count is the metric behind essays, blog posts, tweets, and every 'X min read' label. This guide explains exactly how words and characters are counted, how reading time is estimated, and how to hit a word target without losing meaning.

  2026-09-03

• CSS Units Explained: px, rem, em, %, and When Each One Is the Right Call

  The same length renders differently depending on the unit you write, and picking wrong is how interfaces break at zoom levels you never tested. This guide maps absolute vs relative units, why rem is the accessible default for text, how em compounds (and burns you), the two very different meanings of %, and when vw/dvh are the right call.

  2026-08-24

• JSON Schema Explained: Validation, Types, and the Keywords That Do the Real Work

  JSON is loosely typed, and JSON Schema is the contract that gives it shape. This guide covers the type system, properties/required/additionalProperties, string and number constraints, array rules, composition with oneOf/allOf/$ref, and how schemas power API validation, generated forms, and test data.

  2026-08-24

• AES Encryption Explained: The Algorithm Behind the Padlock, and What It Means for Your Data

  AES is the symmetric cipher that encrypts most of the internet, but a password alone isn't a key, and a key alone isn't secure — the mode and the nonce decide that. This guide explains AES key sizes, password-derived keys, ECB/CBC/GCM modes, and the practical checklist for encrypting your own data.

  2026-08-21

• CSS Gradients Explained: linear, radial, conic, and the Patterns That Actually Look Good

  A CSS gradient is a function, not a color — and until you treat it as one, every gradient you write ends up muddy or banded. This guide covers the linear/radial/conic functions, color stops and the hard-stop trick for stripes, transparent fades, and the four mistakes behind ugly gradients.

  2026-08-21

• CSS Box Shadows Explained: The Five Parts, Layering, and Why Your Shadows Look Off

  box-shadow has five parts, and until you know what each one does, shadows either look flat or muddy. This guide explains the syntax, the inset and layered-shadow tricks that power modern UI, and the design rules that separate a card that looks 'pressed' from one that looks blurry.

  2026-08-18

• Sitemaps and robots.txt Explained: How Search Engines Discover, Crawl, and Index Your Site

  Two files control how search engines see your site, and both are routinely misunderstood. This guide explains robots.txt Allow/Disallow rules and wildcards, why robots.txt cannot hide a page (and what noindex actually does), the structure of an XML sitemap, and the common mistakes that quietly kill discovery.

  2026-08-18

• CSS Flexbox Explained: The Complete Guide to the Flex Layout Model, Alignment, and Gaps

  What's the difference between justify-content and align-items? Why do flex children shrink when you didn't ask them to? This guide explains the flex layout model — main axis, cross axis, alignment, sizing, and gaps — plus the mistakes that confuse developers every day.

  2026-08-17

• CSS Grid Explained: Rows, Columns, Areas, and When to Reach for Grid Instead of Flexbox

  What do fr units actually do? How do grid-template-areas lay out a whole page in ASCII? This guide explains the grid layout model — tracks, lines, placement, and areas — plus the minmax/auto-fit tricks that make responsive layouts effortless.

  2026-08-17

• The Complete curl Command Guide: Every Flag You'll Actually Use

  curl is the fastest way to talk to an HTTP API from the terminal — if you know the flags. This guide covers reading responses, headers and methods, JSON POSTs, file uploads, cookies, verbose debugging, and timeouts, with the exact incantations you'll reuse every day.

  2026-08-17

• HTTP Methods Explained: GET, POST, PUT, PATCH, DELETE and the Semantics That Actually Matter

  What's the difference between PUT and PATCH? Why is a GET request supposed to be harmless? This guide explains the HTTP methods, the safe/idempotent/cacheable distinction, how methods pair with status codes, and the mistakes that silently break caching and retries.

  2026-08-17

• How Diff Works: Unified Diff Format, the Myers Algorithm, and Reading Patches Fluently

  What do @@, +++, and --- mean in a patch? How does a computer find the 'minimal' difference between two files? This guide explains how diff algorithms actually work, how to read unified diff, and why some diffs look wrong.

  2026-08-13

• PNG vs JPG vs WebP vs SVG: How to Choose the Right Image Format Every Time

  Why does a screenshot look terrible as JPG? When is SVG wrong? Is WebP always better? This guide explains how the major image formats compress, what each one is good at, and a decision process you can apply in seconds.

  2026-08-13

• Email Validation Done Right: Why the Perfect Regex Doesn't Exist (and What to Do Instead)

  Is a@b a valid email? What about user+tag@gmail.com or 用户@example.com? This guide explains what RFC 5322 actually allows, why regex validation always disappoints, and the practical validation strategy that actually works.

  2026-08-12

• Binary, Octal, Decimal, Hex: A Developer's Guide to Number Base Conversion

  Why do programmers count in hex? How do you convert 0xFF to decimal without a calculator? What does 0b1010 actually mean? This guide explains positional number systems, conversion methods, and the shortcuts developers use every day.

  2026-08-12

• chmod and Linux File Permissions Explained: What 755, 644, and rwx Really Mean

  What does chmod 755 actually do? Why is 777 dangerous? How do you read rw-r--r--? This guide explains Linux file permissions — the rwx model, octal numbers, ownership, and the special bits — with the rules that keep servers secure.

  2026-08-11

• HEX, RGB, and HSL Color Formats Explained: How to Convert and When to Use Which

  Why is #FF5733 the same color as rgb(255, 87, 51)? What do hue, saturation, and lightness actually control? This guide explains the three web color formats, how to convert between them, and which one to reach for in real CSS work.

  2026-08-11

• Hashing Explained: MD5, SHA-256, and Why Hashing Is Not Encryption

  What is a hash function, really? Why is MD5 broken but still everywhere? When do you need SHA-256, bcrypt, or just a checksum? This guide explains how hashing works, what it's for, and the mistakes that get systems hacked.

  2026-08-10

• CIDR and Subnetting Explained: How to Read 10.0.0.0/24 Without Guessing

  What does /24 actually mean? How many hosts fit in a /26? Why can't you use the first and last address of a subnet? This guide explains CIDR notation, subnet masks, and how to split networks — with a mental method that works without a calculator.

  2026-08-10

• What Base64 Actually Is: Why an Image Turns Into a String of Characters

  Ever opened page source and found an image whose src is a long string starting with iVBOR? That's Base64. This article walks through the 64-character alphabet, the 3-bytes-to-4-characters encoding process step by step, the ~33% size overhead, = padding, the URL-safe variant, and why Base64 is not encryption.

  2026-08-06

• Character Encoding & Unicode Explained: From ASCII to UTF-8, Mojibake, and Beyond

  Why does the same file turn into gibberish in a different editor? What actually separates UTF-8 from UTF-16? This guide walks from ASCII to Unicode, code points, encodings, BOM, normalization, and the practical art of debugging mojibake.

  2026-08-06

• Color Contrast on the Web: A Practical Guide to WCAG

  Why does your light-gray text look fine to you but fail accessibility checks? This guide explains how WCAG contrast ratios are calculated, the difference between AA and AAA, and what to do when your brand color doesn't pass.

  2026-08-06

• The Complete Guide to Cron Expressions: Five Fields, Classic Pitfalls, and Debugging Tips

  Why is `*/5` completely different from `5`? Why is Sunday both 0 and 7? And why does your 2:30 AM job silently vanish one day a year? This guide covers cron syntax, common schedules, and the traps that bite everyone eventually.

  2026-08-06

• Common CSV Problems: Encoding Mojibake, Delimiters, and Excel Traps

  CSV looks simple but is full of traps: garbled characters in Excel, European files using semicolons, IDs turned into scientific notation. This guide explains each common CSV problem and how to fix it.

  2026-08-06

• The Complete Guide to DNS Record Types: From A Records to Troubleshooting

  What do A, AAAA, CNAME, MX, TXT, NS, SOA, CAA, and SRV records actually do? Why can't a CNAME live at your root domain? And why should you lower the TTL before a migration? This guide covers the common record types, TTL caching behavior, and a practical troubleshooting workflow.

  2026-08-06

• HTTP Status Codes Troubleshooting Guide: Where to Look When You See 4xx/5xx

  A status code is the first clue when an API call fails. This guide explains the five status code classes, breaks down the 16 most common codes from 200 to 504 with causes and debugging steps, and clarifies 301 vs 302 for SEO and 502 vs 504.

  2026-08-06

• 10 Common Reasons JSON.parse Fails (and How to Fix Each One)

  Unexpected token, trailing commas, single quotes — JSON error messages are famously unhelpful. This guide breaks down the 10 most common JSON syntax errors and shows you how to spot and fix each one fast.

  2026-08-06

• JWT Explained: The Three-Part Structure, What Signing Proves, and the Classic Mistakes

  What do the three dot-separated parts of a JWT actually contain? Does a signature hide your data? When should you pick HS256 over RS256? This guide covers JWT structure, verification, common claims, pitfalls, and debugging.

  2026-08-06

• The Complete Guide to Markdown Tables: Syntax, Alignment, and Common Pitfalls

  Markdown tables look like a few pipes and dashes, but they come with real gotchas: alignment colons, escaping pipes inside cells, and the hard no-newline rule. This guide covers the full syntax, its limits, and when to stop hand-writing tables.

  2026-08-06

• Password Security in Practice: How Long Is Long Enough?

  Is an 8-character complex password safer than a 16-character random one? This guide uses entropy math to answer the question, and shows how password managers and secure generators make a strong password strategy actually doable.

  2026-08-06

• Regex for Beginners: 10 Patterns You'll Actually Use Every Day

  You don't need to memorize the whole regex spec to solve most real problems. This guide breaks down the 10 most useful everyday patterns symbol by symbol, explains greedy vs. lazy matching, and shows you how to test a regex properly before shipping it.

  2026-08-06

• The Complete Guide to Unix Timestamps: From the Epoch to the 2038 Problem

  Why does time start counting from 1970? What happens when you mix up seconds and milliseconds? And what breaks on January 19, 2038? This guide covers Unix timestamp concepts, common pitfalls, and practical debugging tips.

  2026-08-06

• The Complete Guide to URL Encoding: When to Use encodeURIComponent (and When Not To)

  What does %20 in a URL actually mean? Should you use encodeURI or encodeURIComponent? Why does a space sometimes become a plus sign? This guide covers the rules, the history, and the common traps of URL encoding.

  2026-08-06

• The Complete Guide to UUIDs: v1–v7, Collision Math, and Database Reality

  How many UUID versions are there, really? Will random v4 UUIDs ever collide? Why is v7 the modern default for database primary keys? This guide covers UUID versions, the birthday-paradox math, index implications, and the security mistakes to avoid.

  2026-08-06

• The Complete Guide to YAML Pitfalls: From the Norway Problem to Unsafe Loaders

  Why does Norway's ISO country code become false? Why does version 1.10 turn into 1.1? YAML looks harmless, but its implicit type guessing bites everyone eventually. This guide covers the classic traps, the security risks, and how to defend yourself.

  2026-08-06