All tools

🐞 Code Helpers tools

37 free Code Helpers tools. Each one runs right in your browser: no sign-up, no watermark, and your files stay on your device.

  • 📐 PX to REM Converter Convert CSS sizes between px, rem, em, pt, vw, vh and % with your own base size.
  • 📚 Regex Pattern Library Copy tested regular expressions for common data and test them on your own values.
  • ✅ JSON Validator Check JSON and see the exact line, column and reason of any error, with a one-click fix for common mistakes.
  • 🧾 XML Validator Check that XML is well-formed and see the line and reason of any error, plus a document summary.
  • 🔎 On-Page SEO Checker Paste a page’s HTML to check title, meta description, headings, image alt text, canonical, mobile and social tags.
  • 🧪 HTML, CSS and JS Playground Write HTML, CSS and JavaScript and see the result live in a safe sandbox; download it as one file.
  • ⌨️ JavaScript Console Run JavaScript in a safe sandbox and see results, console.log output and errors.
  • ⚖️ CSS Specificity Calculator Work out the specificity of CSS selectors, including :is, :not, :has and :where, and see which one wins.
  • 🎯 CSS Selector Tester Paste HTML, type a CSS selector, and see exactly which elements it selects.
  • ⬛ Border Radius Generator Round each corner separately or make organic blob shapes, with a live preview and CSS.
  • 🔷 CSS Clip-Path Maker Make clip-path shapes like triangles, hexagons, stars and arrows, drag the points, and copy the CSS.
  • 🎞️ CSS Animation Generator Pick a ready animation (fade, slide, bounce, pulse, shake, spin…), tune the timing and copy the CSS.
  • 📦 Flexbox Playground Try flex-direction, wrap, justify-content, align-items and gap on live boxes and copy the CSS.
  • 🔳 CSS Grid Generator Build CSS grid layouts with columns, rows, gaps and template areas; copy the CSS and HTML.
  • 📋 HTML Table Generator Paste rows from Excel, Google Sheets or CSV and get a clean, accessible HTML table.
  • 🔀 JS Object to JSON Convert JavaScript object literals with unquoted keys, single quotes and comments into valid JSON, or back.
  • 🎹 JavaScript Key Code Finder Press any key to see its event.key, event.code, keyCode, location and modifiers.
  • 🏷️ HTML Tags Reference Every common HTML tag explained in plain words, with an example and a live preview.
  • 🎨 CSS Properties Reference The most used CSS properties explained simply, with clickable values that change a live demo.
  • 📝 HTML Form Builder Add fields, set labels and rules, preview the form and copy clean, accessible HTML.
  • 📧 Email HTML Checker Find code that email apps strip or break: scripts, flexbox, external CSS, relative links, big size.
  • 🩺 Error Message Explainer Paste an error from JavaScript, Python, PHP, Java, SQL, npm, git or a web server to see what it means and how to fix it.
  • 🌿 Git Command Helper Describe what you want to do in git and get the command, with your branch and file names filled in.
  • 🧱 HTML Checker Check HTML for unclosed and mismatched tags, wrong nesting, duplicate ids and attributes, missing alt text and page basics.
  • 🎨 CSS Checker Find CSS typos, unknown properties (with “did you mean”), invalid values, bad selectors and missing ; or braces.
  • 🟨 JavaScript Checker (ESLint) Check JavaScript with the real ESLint: syntax errors, undefined variables, unused code, assignments in conditions and more.
  • 🔷 TypeScript Checker Type-check TypeScript with the official compiler: type errors, missing properties, implicit any, plus the compiled JavaScript.
  • 🐍 Python Checker Find Python syntax, indentation and bracket errors and beginner mistakes, then confirm with real Python in the browser.
  • 🗃️ SQL Checker Check SQL for syntax errors in MySQL, PostgreSQL, SQLite, SQL Server, MariaDB, BigQuery and more, plus risky mistakes.
  • 📐 YAML Validator Validate YAML with the exact line of errors, catch tabs and duplicate keys, and see the parsed data as JSON.
  • 📝 Markdown Checker Lint Markdown for skipped heading levels, broken and empty links, missing alt text, unclosed code blocks and spacing.
  • ♿ Accessibility Checker Check HTML for WCAG problems: alt text, labels, button and link names, headings, language, ARIA, zoom and contrast.
  • ▶️ Run Python Run real Python 3.12 in your browser with input() support, NumPy and pandas on demand, and a Stop button.
  • 🧮 SQL Playground Run SQL queries on a real SQLite database in your browser with sample tables, or open your own .sqlite file.
  • 🌙 Run Lua Run Lua 5.3 code in your browser with print, io.write and io.read, and a time limit that stops endless loops.
  • 💎 Run Ruby Run real Ruby 3.3 in your browser with gets for input, the standard library and a Stop button.
  • ⚡ Emmet Expander Expand Emmet abbreviations like ul>li*3 or m10 into full HTML, JSX or CSS, with the official Emmet engine.