50 guides · free tools inside
Practical guides for the things developers actually look up.
Short explainers on JWTs, cron, JSON, regex, hashing and more. Each one ends with a free tool that runs entirely in your browser — nothing you paste is uploaded.
How to Decode a JWT Safely (Without Sending It to a Server)
A JWT is just three Base64URL strings. Learn how to read one, what each claim means, why decoding is not verifying, and how to inspect tokens without leaking them.
Read guide →What a Cron Expression Actually Means (With Examples)
Five fields, a few special characters, and endless confusion. A plain-English guide to reading and writing cron expressions, with common schedules and the gotchas that cause missed jobs.
Read guide →JSON · 3 minHow to Fix "Unexpected Token" and Other Invalid JSON Errors
The handful of mistakes behind almost every JSON parse error: trailing commas, single quotes, unquoted keys, comments, and stray characters. Learn to spot and fix each one fast.
Read guide →JSON · 3 minJSON vs YAML: When to Use Which
Both formats store structured data, but they excel at different jobs. A practical comparison of syntax, comments, safety, tooling, and the YAML pitfalls that bite people in production.
Read guide →Regex · 3 minRegex Cheatsheet for Beginners (With Copy-Paste Examples)
The regular expression syntax you will actually use: character classes, quantifiers, anchors, groups, and lookaheads, plus tested patterns for dates, colors, and more.
Read guide →Encoding · 3 minBase64 Is Not Encryption (And Other Common Misconceptions)
Base64 turns bytes into text and nothing more. Learn how it works, why it is trivially reversible, what it is genuinely good for, and what to use when you need real secrecy.
Read guide →Security · 3 minHow Strong Should a Password Be? Length vs. Complexity
Length beats cleverness. Learn what actually makes a password hard to crack, why random passphrases work, how much entropy is enough, and a simple rule to follow.
Read guide →Security · 3 minMD5 vs SHA-256: Which Hash Should You Use?
Hashes fingerprint data, but not all are safe. Learn when MD5 is fine, when it is dangerous, why SHA-256 is the default, and why passwords need bcrypt or Argon2 instead.
Read guide →Image · 3 minWhy You Should Remove EXIF Data Before Sharing Photos
Photos carry hidden metadata: camera model, timestamps, and sometimes GPS coordinates. Learn what EXIF contains, when it leaks, and how to strip it without uploading the image.
Read guide →Color · 3 minHow to Check Color Contrast for Accessibility (WCAG Explained)
What WCAG contrast ratios mean, the 4.5:1 and 3:1 thresholds for text and UI, how contrast is calculated, and practical ways to fix low-contrast designs.
Read guide →CSS · 3 minCSS box-shadow: A Practical Guide with Examples
How the CSS box-shadow property works, what each value does, how to layer shadows for soft, realistic depth, and the performance and dark-mode traps to avoid.
Read guide →Time · 3 minUnix Timestamps Explained: Seconds, Milliseconds, and Time Zones
What a Unix timestamp is, how to tell seconds from milliseconds, why it has no time zone, how to convert in code, and the bugs (including the Year 2038 problem) that catch people out.
Read guide →QR · 3 minHow to Make a WiFi QR Code (So Guests Never Ask for the Password)
A WiFi QR code lets guests join your network with one scan. Learn the format behind it, how to handle special characters and hidden networks, and how to generate one without sharing your password with a server.
Read guide →PDF · 2 minHow to Merge PDF Files Without Uploading Them Anywhere
Combine several PDFs into one document directly in your browser. Learn the steps, what happens to bookmarks and forms, and why local merging matters for contracts and IDs.
Read guide →PDF · 2 minHow to Compress a PDF Without Losing Quality
Why PDFs get so large, what compression can safely remove, and practical settings for email, web, and print, so you shrink the file without ruining the pages.
Read guide →PDF · 2 minHow to Split a PDF Into Separate Pages or Sections
Split a PDF into single pages or page ranges, extract just the pages you need, and avoid the usual pitfalls with bookmarks and encrypted files.
Read guide →PDF · 2 minHow to Sign a PDF Without Printing It (And What Counts as a Valid Signature)
Draw or place a signature on a PDF in your browser, and understand the difference between a simple image signature and a cryptographic digital signature.
Read guide →PDF · 2 minHow to Convert PDF Pages to Images (PNG or JPEG) at the Right Resolution
Turn each page of a PDF into a PNG or JPEG, choose the right DPI for screens or print, and understand when to pick PNG over JPEG.
Read guide →Image · 2 minHow to Resize an Image Without Losing Quality
The difference between resizing and compressing, how to keep images sharp, which format to choose, and the sizes to use for web and retina screens.
Read guide →Image · 2 minHow to Crop an Image to a Specific Aspect Ratio (1:1, 4:3, 16:9 and More)
What aspect ratios mean, the common ones for social media, thumbnails, and link previews, and how to crop without cutting off the subject.
Read guide →Image · 2 minHow to Make a Favicon for Your Website (Sizes, Formats, and HTML)
Everything you need for a modern favicon: the sizes browsers and phones ask for, ICO vs PNG vs SVG, and the exact HTML to add.
Read guide →Image · 2 minHow to Convert an Image to Base64 (Data URLs): When It Helps and When It Hurts
Embed small images directly in HTML or CSS with a Base64 data URL. Learn the syntax, the 33% size penalty, and when a normal image file is the better choice.
Read guide →QR · 2 minQR Code Best Practices: Size, Contrast, Error Correction, and Testing
Make QR codes that actually scan. Learn about error-correction levels, the quiet zone, minimum size, contrast, static vs dynamic codes, and how to test before you print.
Read guide →QR · 2 minHow to Make a vCard QR Code for Your Contact Details
Let people save your name, phone, and email with one scan. Learn the vCard format, what to include, and how to keep the code small enough to scan reliably.
Read guide →JSON · 2 minHow to Convert JSON to CSV (Nested Data, Arrays, and Excel Gotchas)
Flatten JSON into a spreadsheet-ready CSV. Learn how to handle nested objects and arrays, quote values correctly, and avoid the common Excel encoding problems.
Read guide →JSON · 2 minJSONPath Cheatsheet: Query JSON Like You Query XML
A practical JSONPath reference: root, child, wildcard, recursive descent, array slices, and filters, with a worked example and notes on implementation differences.
Read guide →JSON · 2 minJSON Schema for Beginners: Validate Your Data with a Few Keywords
What JSON Schema is, the handful of keywords you need (type, properties, required, enum, minimum), and how to write and test a schema for real data.
Read guide →JSON · 2 minHow to Convert JSON to TypeScript Interfaces (and Why Types Aren't Enough)
Generate TypeScript types from a JSON sample, handle optional fields, nulls, and unions, and learn why runtime validation still matters.
Read guide →JSON · 2 minHow to Compare Two JSON Files (Semantic Diff vs Text Diff)
Why a plain text diff is noisy for JSON, how a semantic diff ignores key order and whitespace, and how to read added, removed, and changed values.
Read guide →Color · 2 minHEX vs RGB vs HSL: Which Color Format Should You Use in CSS?
How hex, RGB, and HSL describe the same colors, how to convert between them, and why HSL is easiest for building palettes and hover states.
Read guide →Color · 2 minHow to Choose a Color Palette for a Website or App (A Simple Method)
A practical, repeatable way to build a palette: pick a brand color, add neutrals and accents, create shade scales, and check contrast so it's accessible.
Read guide →CSS · 2 minCSS Flexbox Cheatsheet: Every Property Explained with Examples
A compact reference for Flexbox: container properties, item properties, the flex shorthand, and copy-paste patterns for centering, navbars, and equal columns.
Read guide →CSS · 2 minCSS Grid vs Flexbox: When to Use Which (With Layout Examples)
Flexbox is one-dimensional and Grid is two-dimensional. Learn how to choose, plus a responsive card grid with auto-fit and minmax, and how to combine both.
Read guide →CSS · 2 minHow to Create the Glassmorphism (Frosted Glass) Effect with CSS
Build a frosted-glass card with backdrop-filter, a translucent background, and a subtle border, plus the accessibility and performance points to watch.
Read guide →CSS · 2 minFluid Typography with CSS clamp(): Scale Text Smoothly Without Media Queries
Use clamp() to make font sizes grow smoothly between a minimum and maximum, with the formula, ready-to-use values, and how to keep text accessible when users zoom.
Read guide →Text · 2 minHow to Remove Duplicate Lines from Text (Online, Excel, and the Command Line)
Deduplicate lists of emails, URLs, or log lines. Options for keeping order or sorting, ignoring case and whitespace, plus one-line commands for terminal and code.
Read guide →Text · 2 mincamelCase, snake_case, kebab-case, PascalCase: Naming Conventions Explained
What each text case style is, where it's used in JavaScript, Python, CSS, URLs, and constants, and how to convert between them safely.
Read guide →Markdown · 2 minMarkdown Cheatsheet: Every Syntax You Need (With Examples)
A complete quick reference for Markdown: headings, emphasis, lists, links, images, code blocks, quotes, tables, task lists, and how to escape special characters.
Read guide →Markdown · 2 minHow to Make a Markdown Table (Alignment, Escaping, and Limits)
Write tables in Markdown with pipes and dashes, align columns, escape pipe characters, and learn what tables can't do, with tips for generating large ones.
Read guide →Security · 2 minHow to Verify a File Checksum (SHA-256) on Windows, macOS, and Linux
Check that a download is complete and untampered by comparing its SHA-256 hash, with commands for every operating system and what a mismatch means.
Read guide →Security · 2 minbcrypt vs Argon2: How to Hash Passwords Properly
Why passwords need slow, salted hashes, how bcrypt and Argon2id differ, sensible parameters, and how to migrate an existing user database.
Read guide →Time · 2 minTime Zone Conversion: 7 Mistakes That Break Schedules and Timestamps
Store UTC, use IANA zone names, respect daylight saving, and avoid ambiguous abbreviations like EST. The practical rules for handling time zones correctly.
Read guide →Convert · 2 minBinary, Octal, Decimal, and Hexadecimal Explained (With Conversion Methods)
How number bases work, how to convert between binary, decimal, and hex by hand, and why programmers use hex for colors, memory, and bytes.
Read guide →Calculators · 2 minHow Loan EMI Is Calculated: The Formula, a Worked Example, and How to Reduce It
The EMI formula explained step by step, a worked home-loan example with total interest, how tenure and rate change payments, and how prepayment helps.
Read guide →Calculators · 2 minCompound Interest Explained: The Formula, the Rule of 72, and Why Time Matters
How compound interest grows money faster than simple interest, the formula with a worked example, the effect of compounding frequency, and the rule of 72.
Read guide →Developer · 2 minHTTP Status Codes Cheatsheet: What 200, 301, 404, 500 and the Rest Mean
A practical guide to the HTTP status codes you'll meet: the five classes, the most common codes, how 401 differs from 403, and which redirects to use.
Read guide →Developer · 2 minUUID Versions Explained: v1, v4, v5, v7 and Which One to Use
What a UUID is, how the versions differ, whether collisions are a real risk, and why time-ordered UUIDv7 is friendlier to databases than random v4.
Read guide →Developer · 2 minHow to Write a .gitignore File: Patterns, Examples, and Common Mistakes
Learn .gitignore pattern syntax, what belongs in it, how to stop tracking files you already committed, and how to keep secrets out of your repository.
Read guide →Encoding · 2 minURL Encoding (Percent-Encoding) Explained: encodeURIComponent, Spaces, and Double Encoding
Why URLs need encoding, which characters are reserved, the difference between encodeURI and encodeURIComponent, %20 versus +, and how to avoid double encoding.
Read guide →Security · 2 minHow to Generate a Secure API Key or Secret (Length, Encoding, and Storage)
How much randomness an API key needs, why to use a cryptographic random generator, how to encode and prefix keys, and how to store and rotate them safely.
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