All Free Online Developer Tools & Utilities

Calendar-accurate age between any two dates — years, months, days plus total weeks, hours, seconds, and next-birthday countdown

Audit any page for missing alt text and broken images, then export clean Markdown reports

Three-way calculator — lock any of ratio, width, or height and compute the other two. Visual rectangle preview, eleven preset ratios (YouTube/TikTok/Instagram/Open Graph/Cinemascope), and GCD-based reduction

Decode Base64 strings back to readable plain text safely

Convert plain text to Base64 format instantly with Unicode support

Decode Base64 strings back to downloadable image files

Body Mass Index with metric or imperial units, WHO categories, and healthy weight range for your height

Estimate body fat percentage from tape-measure values (neck, waist, hip, height) using the US Navy circumference method with ACE body-fat category lookup, lean and fat mass output, and metric or imperial units

Visual CSS border-radius builder with elliptical per-corner control and auto-shorthand output

Mifflin-St Jeor BMR + TDEE with five activity levels and per-goal daily calorie targets for maintenance, fat loss, and muscle gain

Convert text between uppercase, lowercase, title case, and more

Test color pairs against WCAG 2.2 AA/AAA accessibility standards with live preview

Convert between HEX, RGB, HSL, and other color formats

Blend two colors with sRGB linear, HSL midpoint, or perceptually-uniform OKLCH interpolation. Live preview, 9-step gradient strip, HEX/RGB/HSL output. CSS Color 4 standard.

Generate beautiful color palettes for your projects

Pick exact pixel colors from any uploaded image with HEX, RGB, and HSL output, WCAG contrast ratios against black and white, and native EyeDropper API support for picking colors anywhere on screen (Chromium)

Future value of any savings or investment account with regular contributions and seven compounding frequencies

Write, parse, and validate any standard 5-field cron schedule with next-fire times and plain-English description

Format minified CSS into clean, readable code with proper indentation

Multi-layer box shadow builder with per-layer offset, blur, spread, color, alpha, and inset control plus Tailwind and Material presets

Build polygon, inset, circle, and ellipse CSS clip-paths with a vertex editor and ten shape presets

Visual builder for the full CSS filter property — blur, brightness, contrast, grayscale, hue-rotate, invert, opacity, saturate, sepia — with live before/after preview, six presets, and CSS plus Tailwind v4 output

Visual builder for linear, radial, and conic CSS gradients with live preview and Tailwind/SCSS export

Minify and compress CSS code to reduce file size

Parse any CSS selector and compute its specificity (a, b, c) per CSS Selectors Level 4. Handles :is, :not, :has, :where, attribute selectors, pseudo-elements. Compare-two-selectors mode shows which wins the cascade.

Bidirectional CSV ↔ JSON converter with RFC 4180 quoting, custom delimiters, and smart type inference

Convert CSV to a clean JSON array of objects. Handles quoted fields, custom delimiters, headers, and optional type inference. Runs 100% in-browser.

Exact difference between two dates in days, weeks, calendar Y/M/D, business days, hours, and minutes — plus a date-arithmetic mode for adding or subtracting years/months/weeks/days from a base date

Compare two texts and highlight differences

Convert one image into every favicon size browsers, iOS, and Android need — 16, 32, 48, 96, 180 (Apple Touch), 192 and 512 (PWA). Includes copy-paste HTML head snippet and site.webmanifest

Find and replace text with optional ECMAScript regex (including $1/$2 capture-group backreferences), case-insensitive, whole-word, and multiline modes. Live match count, recipe presets, in-place chain apply.

Visual CSS flexbox playground with controls for flex-direction, justify-content, align-items, flex-wrap, and gap. Adjustable item count (1-12), four presets, live preview, and CSS plus Tailwind v4 output

Visual builder for the iOS-style frosted-glass CSS effect with backdrop-filter blur, saturation, transparency, border, and shadow. Four presets, live preview over four background types, vanilla CSS and Tailwind v4 output

Weighted and unweighted GPA across the 4.0 and 5.0 scales with full letter grades, P/NP/W exclusion, and per-course contribution breakdown

Visual CSS Grid playground with editable column and row tracks, gap and alignment controls, four presets (3-Column Equal, Sidebar+Content, Holy Grail, Auto-Fit Cards), live preview, and CSS plus Tailwind v4 output

Generate MD5, SHA-1, SHA-256, and SHA-512 hashes instantly

Compute HMAC signatures (SHA-1, SHA-256, SHA-384, SHA-512) via the Web Crypto API with hex, Base64, and Base64URL output. Used for JWT HS256, AWS Sig V4, GitHub webhooks, and API request signing.

Bidirectional HTML entity encoder and decoder with four modes, decimal/hex numeric output, and full surrogate-pair Unicode support

Format and beautify HTML code with proper indentation

Convert HTML to React JSX: 30+ attribute renames (class→className, for→htmlFor, event handlers to camelCase), inline styles to object syntax, void elements self-closed, HTML comments translated.

Complete searchable reference for every HTTP status code (1xx-5xx) with plain-English descriptions, typical use cases, and RFC 9110 citations — including WebDAV, rate-limit, and captive-portal extensions

Reduce JPG, PNG, and WebP file size by 50-90% via the Canvas API in your browser. Adjustable quality, max-width downscale, JPEG/WebP/PNG output, live before/after byte comparison, one-click download. No uploads.

Convert images to Base64 encoded strings (Data URI) instantly

Minify and compress JavaScript code for production

Semantic JSON comparison — walk two JSON trees and emit path-indexed added / removed / changed records. Ignores whitespace and key order. Distinct from line-by-line text Diff Checker.

Format, validate, and beautify JSON data with advanced error handling

Generate JSON Schema (Draft 2020-12, 2019-09, or Draft-07) from any JSON example with inferred types, required fields, and detected string formats (email, uuid, date-time, uri, ipv4).

Convert a JSON array of objects to CSV instantly. Flatten nested keys, choose a delimiter, and get RFC 4180-quoted output. 100% in your browser.

Generate clean TypeScript interfaces from any JSON with recursive nested types, array unions, and configurable style

Bidirectional JSON ↔ YAML converter with custom serializer and YAML 1.2 subset parser tuned for real-world configs (Kubernetes, GitHub Actions, Docker Compose, Ansible). Inline error reporting and one-click direction toggle.

Decode JSON Web Tokens to inspect header, payload, and claims with expiration check — 100% client-side

Estimate token count and API cost for any prompt across GPT-4, GPT-4o, Claude Opus 4.7, Claude Sonnet 4.6, Claude Haiku, Gemini 1.5 Pro and Flash. Live count, 2026 pricing, context-window utilization bar

Auto, personal, student, and credit-card payoff loan calculator with side-by-side term-length comparison, monthly payment, total interest, and full month-by-month amortization schedule

Generate placeholder text for designs and mockups

Preview and edit Markdown with live rendering

Visual GFM Markdown table builder with paste-from-spreadsheet import, per-column alignment, and pipe-escape safety

Convert Markdown to clean HTML with side-by-side rendered preview. Supports CommonMark essentials plus GFM strikethrough, fenced code, and tables. 100% client-side custom parser.

Extract a table of contents from any Markdown document with GitHub-, GitLab-, or Pandoc-style heading anchors. Configurable depth, duplicate-slug handling, ordered or unordered list, base-level normalization.

Paste HTML and see live Google SERP, X, Facebook, and LinkedIn previews with length checks and per-rule SEO validation

Fixed-rate mortgage calculator with monthly payment, total interest, year-by-year schedule, and extra-payment savings comparison

Convert numbers between binary, octal, decimal, hexadecimal, and any base 2-36 with BigInt precision and two's complement support

Generate HTML <head> meta tags for Open Graph (Facebook/LinkedIn/Slack), Twitter Card, description, canonical, and theme-color from a simple form. Character-count guidance based on 2026 platform best practices.

Generate strong, secure passwords with custom options

Offline password strength tester with entropy math, breach-corpus check, pattern detection, and crack-time estimates

Five percentage operations in one tool — X% of Y, X as % of Y, percent change, add/subtract a percent — with formula breakdown

Classic 25-minute focus and 5-minute break Pomodoro timer with long-break-every-fourth-session cycle, four built-in presets (Classic, Short Focus, Deep Work 90/20, 52/17), browser notifications, and configurable durations

Convert pixels to rem units instantly with a custom base font size, plus a px-to-rem reference table for responsive, accessible CSS.

Generate QR codes for URLs, text, and more

Cryptographically-strong random integers in any range with no modulo bias — up to 10,000 numbers, optional uniqueness and sort

Estimate reading and speaking time for any text at an adjustable words-per-minute. Counts words and characters instantly in your browser.

Test and debug regular expressions with live matching

Convert rem units to pixels instantly with a custom root font size, plus a rem-to-px reference table for precise, predictable CSS sizing.

Remove duplicate lines from any list, keeping the first occurrence. Case-insensitive and trim options, plus optional alphabetical sort.

Remove line breaks from text instantly — replace with spaces, strip entirely, or keep paragraphs. Handles Windows, Mac, and Unix line endings.

Format and beautify SQL queries with syntax highlighting

Encode SVG markup to a Base64 or URL-encoded data URI with a ready CSS snippet, and see which is smaller. Free, client-side, no uploads.

Sort lines alphabetically, numerically, by length, in reverse, or randomly shuffle. Optional case-insensitive, deduplication, whitespace trimming. Crypto-strength Fisher-Yates shuffle.

Convert any time between IANA timezones with a live world-clock board showing nine cities at once. DST-aware offsets, 12/24-hour toggle, ISO 8601 output, and full IANA timezone database

Convert between Unix timestamps and human-readable dates

Calculate tip and split the bill across any party size — pre-tax or post-tax mode, optional round-up, per-person breakdown

Universal unit converter across seven categories — length, weight, volume, temperature, area, speed, time — with NIST-exact factors

Encode and decode URLs for web development

Decompose any URL into protocol, host, port, path segments, query parameters (as a table), and hash using the native WHATWG URL parser. Decoded and raw values shown side-by-side.

Turn any title into a clean, lowercase, diacritic-free, RFC 3986-safe URL slug with separator, case, and stop-word controls

Generate unique UUIDs (v1, v4, v5) for your applications

Daily water requirement by body weight, activity level, and climate with output in liters, fluid ounces, cups, and 500 ml bottles plus a recommended hourly drinking schedule

Count words, characters, and reading time for any text

Beautify or minify XML with native DOMParser validation. Works on SOAP envelopes, RSS feeds, sitemaps, Android string resources, SVG, and Office Open XML. 100% client-side.

Validate, format, and convert YAML with line-precise errors — ideal for GitHub Actions, Kubernetes, Docker Compose, and Ansible