64 guides

Guides & tutorials

Clear, practical walkthroughs for the everyday developer tasks behind every tool on filemarkr.

JSON & Data

How to Format and Pretty-Print JSON (Without Breaking It)

Learn how to pretty-print messy JSON, indent it correctly, spot syntax errors fast, and read deeply nested data with a live tree view in your browser.

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JSON & Data

How to Minify JSON and Shrink Your API Payloads

Minify JSON to cut payload size, speed up API responses, and save bandwidth. See how whitespace stripping works, real byte savings, and pitfalls to avoid.

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JSON & Data

How to Validate JSON and Pinpoint the Exact Syntax Error

Validate JSON syntax and jump to the exact line and column of any error. Learn the rules, the most common mistakes, and how to debug malformed JSON fast.

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JSON & Data

How to Convert JSON to CSV for Excel and Google Sheets

Convert a JSON array of objects into clean CSV ready for Excel or Sheets. Learn how flattening works, how to handle nested fields, and pitfalls to avoid.

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JSON & Data

How to Convert CSV to JSON (With Proper Header Detection)

Turn CSV rows into a clean JSON array of objects with automatic header detection. Learn parsing rules, quoting, type handling, and common pitfalls.

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Encode & Decode

How to Convert an Image to a Base64 Data URI (and When You Actually Should)

Learn how to encode any image as a Base64 data URI for inline CSS, HTML, and JSON, with real examples, size math, and the tradeoffs to watch for.

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Encode & Decode

URL Encoding Explained: Percent-Encode Query Strings Without Breaking Them

Understand percent-encoding, when to use encodeURIComponent vs encodeURI, and how to safely encode and decode query-string values and URLs in the browser.

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Encode & Decode

HTML Entities Explained: Escape Markup So Your Text Renders, Not Executes

Learn how HTML entity encoding works, which characters to escape, why order matters, and how to safely display code and special symbols in HTML.

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Encode & Decode

How to Decode a JWT and Read Its Claims (Without a Library)

Understand the three parts of a JSON Web Token, decode the header and payload by hand, check expiry, and learn why decoding is not the same as verifying.

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Encode & Decode

How to Parse a URL Into Its Parts: Protocol, Host, Path, Query, and Hash

Break any URL into protocol, host, port, path, query parameters, and hash. Learn the URL anatomy and how the browser's URL API parses it correctly.

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Converters

How to Convert HTML to Clean Markdown for Docs and Issues

Learn how HTML-to-Markdown conversion works, walk through a real example, and avoid the table and whitespace pitfalls that trip most people up.

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Converters

Roman Numerals Explained: Convert Numbers Both Ways (Up to 3,999,999)

Understand how Roman numerals work, the subtractive rules, and the vinculum trick that lets you convert numbers up to 3,999,999 both ways.

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Converters

Text to Binary: How Characters Become Bits (and Back Again)

See exactly how text turns into binary, hex, octal and decimal through character encoding, with runnable examples and Unicode gotchas explained.

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Encode & Decode

Base64 Encoding Explained: Encode and Decode Text the Right Way

Understand what Base64 does, why btoa breaks on Unicode, and how to encode and decode text correctly with a full-Unicode, browser-only tool.

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Encode & Decode

Base64 to Image: Preview and Save Pictures from a Data URI String

Got a long Base64 blob and no idea what image it is? Learn how data URIs work and how to preview, verify and download the picture in seconds.

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JSON & Data

How to Diff Two JSON Files and Actually See What Changed

Comparing JSON by eye is painful and text diffs choke on key order. Learn how structural JSON diffing works and spot every added, removed or changed value.

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Converters

Binary, Octal, Hex, Decimal: A Practical Guide to Number Base Conversion

Hex, binary and octal show up in colors, permissions and bitmasks. Learn how base conversion works and convert between all four bases without mistakes.

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Converters

HEX, RGB, HSL, HSV: How to Convert Colors and When to Use Each

HEX, RGB, HSL and HSV each solve a different problem. Learn how to convert colors between them, when to use each and how to avoid rounding mistakes.

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Converters

Turn CSV Into a Clean Markdown Table for Your README

Aligning Markdown table pipes by hand is tedious. Learn how GitHub-flavored tables work and turn any CSV into a clean, ready-to-paste Markdown table.

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Converters

How to Convert Markdown to Clean, Safe HTML

Need HTML from Markdown for a CMS, email or static site? Learn how Markdown parsing works, why sanitizing matters and how to get clean, safe HTML.

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Encode & Decode

How to Escape and Unescape Strings for JSON and JavaScript

Learn how backslash escaping works in JSON, JavaScript and other languages, and how to safely escape or unescape any string right in your browser.

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Format & Minify

How to Format Messy SQL Queries into Readable Code

Turn one-line, unreadable SQL into clean, indented queries. Learn SQL formatting rules for MySQL, Postgres and more, and beautify queries in your browser.

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Format & Minify

How to Pretty-Print and Format XML for Readability

Pretty-print messy XML into clean, indented markup, or minify it back to one line. Learn XML formatting basics and format XML privately in your browser.

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Format & Minify

How to Beautify Messy HTML into Clean, Readable Markup

Learn how to format and indent minified or messy HTML into clean, readable markup, then beautify your markup instantly and privately in your browser.

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Format & Minify

How to Beautify and Format Messy CSS

Turn minified or inconsistent CSS into clean, well-indented styles. Learn CSS formatting conventions and beautify CSS instantly in your browser.

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Text Tools

How to Find and Replace Text with Regex (Without Firing Up an Editor)

Learn plain-text and regex find and replace, capture groups, backreferences, and case-insensitive matching in a fast, private, browser-based tool.

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Text Tools

Reverse Text the Right Way: Characters, Words, Lines, and Unicode Gotchas

Reverse strings by character, word, or line in your browser. Learn why naive JavaScript reversal breaks emoji and how to flip text safely and privately.

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Text Tools

Write Better Markdown Fast: A Live-Preview Editor Guide with Syntax Cheatsheet

A practical guide to writing Markdown with a live side-by-side preview: headings, lists, code fences, tables, and links, all rendered privately in your browser.

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Text Tools

How to Remove Line Breaks and Clean Up Messy Whitespace in Text

Strip unwanted line breaks, join wrapped paragraphs, and collapse extra whitespace fast. Learn the difference between CR, LF, and CRLF and when to keep them.

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Generators

UUID v4 vs v1: How to Generate Unique IDs in Bulk (and When to Use Each)

Generate v4 and v1 UUIDs in bulk right in your browser. Understand the version differences, collision odds, and when to pick random vs. time-based IDs.

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Generators

How to Generate Strong Random Passwords (and What Actually Makes One Strong)

Learn what makes a password strong, how entropy really works, and how to generate secure random passwords in your browser with full control.

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Generators

Lorem Ipsum Explained: How to Use Placeholder Text Without Wrecking Your Layout

What Lorem Ipsum is, why designers still use it, and how to generate the right amount of placeholder text for mockups, prototypes and CMS testing.

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Generators

How to Create a QR Code From Any Link or Text (No App Required)

Learn how QR codes actually encode data, how to generate one from a URL or text in your browser, and how to keep it reliably scannable.

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Generators

How to Generate Random Numbers in a Range (Unique, Sorted, and Fair)

A practical guide to generating random numbers in any range, drawing unique values without repeats, and avoiding common off-by-one and bias mistakes.

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Generators

NanoID Explained: Compact, URL-Safe IDs With a Custom Alphabet and Size

Understand how NanoID works, why it beats UUID for URLs, and how to pick a safe size and alphabet to keep collisions vanishingly unlikely.

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Format & Minify

How to Beautify Minified or Messy JavaScript (Without Changing What It Does)

Learn how to beautify minified or messy JavaScript with correct indentation and spacing using a free, browser-based formatter that keeps your code private.

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Format & Minify

How to Minify CSS: Strip Comments and Whitespace to Cut Stylesheet Size

Learn how CSS minification works, what a safe minifier strips, and how to shrink your stylesheet bytes with a free, private, browser-only CSS minifier tool.

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Format & Minify

How to Minify JavaScript with Terser to Cut Your Bundle Size

Learn how JavaScript minification and Terser's compress and mangle work, then shrink your bundle size with a free, browser-based JS minifier that stays private.

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Format & Minify

How to Minify HTML: Remove Comments and Collapse Whitespace Safely

Learn how HTML minification removes comments and collapses whitespace safely, and how to compress your pages with a free, browser-only HTML minifier tool.

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Text Tools

How to Compare Two Blocks of Text and Spot Every Difference

Learn how to compare two blocks of text and highlight every added, removed, or changed line or word with a free, private, browser-based text diff checker tool.

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JSON & Data

How to Convert JSON to YAML for Configs, CI Pipelines and Kubernetes Manifests

Convert JSON to clean, readable YAML for Kubernetes manifests, CI files and configs. Mapping rules, a worked example and cross-parser pitfalls explained.

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JSON & Data

How to Convert YAML to JSON (and Catch Config Errors Before They Ship)

Convert YAML to JSON in your browser and validate configs as you go. Learn the type gotchas, multi-document rules and a worked example with indentation.

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JSON & Data

How to Convert JSON to Well-Formed XML for SOAP, RSS and Legacy APIs

Turn JSON into well-formed, indented XML for SOAP, RSS and legacy APIs. See how objects, arrays and null map to elements, plus escaping and root tags.

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JSON & Data

How to Parse XML into Clean JSON: Attributes, Arrays and Text Nodes Explained

Parse XML into clean JSON in the browser. Learn how attributes, repeated tags and text nodes map, with a worked example and the shape-shifting gotcha.

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JSON & Data

How to Generate TypeScript Interfaces from a JSON API Response

Generate TypeScript interfaces from any JSON API response instantly. Learn how nested objects, arrays and optional fields are inferred — plus the limits.

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Text Tools

camelCase, snake_case, kebab-case: How to Convert Between Naming Styles

Learn how camelCase, snake_case, kebab-case and Title Case differ, when to use each, and how to convert between naming styles right in your browser.

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Text Tools

How to Count Words, Characters and Reading Time Accurately

Count words, characters, sentences, lines and reading time as you type, and learn the edge cases that make accurate counting harder than it looks.

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Text Tools

How to Generate Clean, URL-Safe Slugs from Any Title

Turn any title into a clean, URL-safe slug: lowercase, strip accents and punctuation, and collapse spaces into hyphens, all locally in your browser.

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Text Tools

How to Remove Duplicate Lines from Text (Fast and In-Browser)

Strip duplicate lines from any list or log, with optional trimming, case-insensitive matching and sorting, without uploading your data anywhere.

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Text Tools

How to Sort Lines of Text Alphabetically or Numerically

Sort lines of text alphabetically, numerically or in reverse, with case and locale options, and avoid the classic lexicographic sorting mistakes.

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Dev Utilities

How to Generate MD5, SHA-256 and SHA-512 Hashes (and When to Use Each)

Learn how cryptographic hashing works, generate MD5, SHA-1, SHA-256 and SHA-512 digests in the browser, and know which algorithm fits your task.

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Dev Utilities

How to Hash Passwords with Bcrypt: Salts, Cost Factors and Verification

A practical guide to bcrypt password hashing: why it beats SHA-256, how salts and cost factors work, and how to generate and verify a bcrypt hash.

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Dev Utilities

HTTP Status Codes Explained: A Developer's Cheat Sheet for 1xx to 5xx

Understand every HTTP status code class from 1xx to 5xx, learn the ones that actually matter for APIs, and know exactly which code to return and when.

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Dev Utilities

How to Find and Copy the Exact Path to Any Value in a JSON Tree

Stop guessing at nested JSON. Learn how JSON path notation works and how to explore an API response and copy the precise path to any value in seconds.

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Web & Design

How to Write Meta Tags That Actually Help SEO and Social Sharing

Learn how to write meta tags for SEO, Open Graph and Twitter Cards so pages rank cleanly and unfurl into rich previews on every social platform.

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Time & Date

Unix Timestamps Explained: Convert Epoch Time to Human Dates

Understand Unix epoch time, convert timestamps to human dates and back, and avoid the seconds-versus-milliseconds bugs that quietly break apps.

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Time & Date

How to Read a Cron Expression Without Guessing

Learn to read any cron expression field by field, decode the special characters, and preview the next run times before you trust a schedule.

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Time & Date

Build a Cron Schedule Without Memorizing the Syntax

Build a correct cron schedule with simple controls instead of memorizing crontab syntax, then copy the expression straight into your job runner.

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Dev Utilities

How to Test a Regular Expression Before It Breaks Production

Learn how to test regular expressions with live match highlighting, understand flags and groups, and avoid greedy matches and catastrophic backtracking.

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Generators

How to Write a .gitignore That Actually Keeps Your Repo Clean

Learn how .gitignore rules work and generate a clean file for Node, Python, Go, Rust, macOS and more in seconds — free, private, in your browser.

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Web & Design

CSS box-shadow Explained: Build Realistic Shadows Visually

Understand the CSS box-shadow syntax — offset, blur, spread and inset — then design and copy production-ready shadows with a live visual editor.

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Web & Design

How to Create CSS Gradients: Linear, Radial and Color Stops

Learn CSS linear and radial gradient syntax, angles and multi-color stops, then design and copy smooth gradients with a live browser preview.

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Web & Design

HEX, RGB and HSL: Convert Colors and Build Palettes Fast

Convert colors between HEX, RGB and HSL and generate tints, shades and complementary palettes instantly in your browser — free and private.

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Web & Design

How to Check Color Contrast for WCAG AA and AAA Accessibility

Learn the WCAG contrast-ratio formula and check any text and background pair against AA and AAA standards with a free, private browser tool.

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