Free Web Developer Tools
All the tools you need to validate, format, check, and optimize your HTML, CSS, and web pages. Free, fast, and no registration required.
Validation
HTML Validator
Validate your HTML against the living standard. A quality score, every error with its line, and an automatic fix re-checked until it passes.
Use tool →CSS Validator
Check your CSS for syntax errors, invalid properties, and incorrect values. Quality score with detailed reports.
Use tool →HTML5 Validator
Validate against the latest HTML5 specification. Catch deprecated elements, missing attributes, and spec violations.
Use tool →JSON Validator & Formatter
Validate and format JSON data. Check for syntax errors and get properly indented output.
Use tool →Schema Markup Validator
Test JSON-LD and microdata against the schema.org vocabulary and the properties Google requires for each rich result. Errors only where Google says required.
Use tool →XML Validator
Validate XML files for well-formedness. Check for unclosed tags, mismatched elements, and syntax errors.
Use tool →Whole-Site Scan
Every page of a site read for HTML, accessibility, CSS and metadata issues. Free score and top five issues, no card.
Use tool →Formatting
HTML Formatter & Beautifier
Format, beautify, or minify your HTML. Customizable indentation with 2 spaces, 4 spaces, or tabs.
Use tool →HTML Viewer & Preview
Paste HTML and see it rendered at desktop, tablet or phone width, in a sandbox isolated from this site, with the validator's verdict on the same code.
Use tool →JSON Formatter & Beautifier
Beautify, minify or sort the keys of your JSON, in your browser. Only whitespace changes: large numbers and repeated keys stay exactly as written.
Use tool →JSON Viewer
Explore JSON as a collapsible tree in your browser. Search keys and values, copy the JSONPath or JavaScript path of any value; big numbers stay exact.
Use tool →JSON Compare & Diff
Compare two JSON documents: every added, removed and changed value with its path. Ignores key order, keeps large numbers exact, exports a JSON Patch.
Use tool →CSS Formatter, Beautifier & Minifier
Beautify CSS, or minify it with output checked to render the same on Bootstrap, Pico and Bulma. Keeps licence comments and older Safari support.
Use tool →XML Formatter & Beautifier
Pretty print or minify XML in your browser: sitemaps, feeds, configs, SVG. Text, attributes, comments and CDATA stay exactly as written.
Use tool →HTML Entity Encoder & Decoder
Encode text to HTML entities or decode them back, in your browser, with a reference of every common special character.
Use tool →SEO
Meta Tag Checker
Analyze your HTML meta tags for SEO. Check title, description, viewport, Open Graph, and Twitter Card tags.
Use tool →Open Graph Checker
Test how your page looks when shared on social media. Preview Facebook, Twitter, LinkedIn, and Slack cards.
Use tool →Robots.txt Generator
Write a robots.txt from a form: blocked paths, exceptions, AI crawlers and sitemaps. Every file is read back by an RFC 9309 parser and tested before you copy it.
Use tool →Robots.txt Checker
Test your robots.txt file. Check which pages are blocked from crawlers, find sitemaps, and identify issues.
Use tool →Page Size Checker
Analyze the weight and size of any web page. Check compression, cache headers, and load time.
Use tool →HTTP Status & Redirect Checker
See a URL's status code and every redirect on the way, hop by hop, with what each code means for Google.
Use tool →Accessibility
Accessibility Checker
Find accessibility issues in your HTML. Check alt attributes, heading hierarchy, ARIA labels, and WCAG compliance.
Use tool →Color Contrast Checker
Check text and background colours against WCAG 2.2 AA and AAA, for normal text, large text and UI components, and get the closest colour that passes.
Use tool →Accessibility Monitoring
Keep a site clean: every page re-read every week, the full report of every scan, automatic fixes and API calls included. From 49 EUR a month.
Use tool →Learning
HTML Errors Guide
Learn about the most common HTML errors and how to fix them. Wrong vs correct code examples for each issue.
Use tool →CSS Errors Guide
Unknown properties, invalid values, broken media queries. What each CSS error means and the fix for it.
Use tool →Accessibility Errors Guide
Missing alt text, unlabelled form fields, frames with no accessible name. What each WCAG failure means for a screen reader user.
Use tool →JSON Errors Guide
Unexpected token, trailing comma, missing bracket. The parser messages you get and what actually caused them.
Use tool →XML Errors Guide
Mismatched tags, multiple root elements, undeclared entities. Why the parser refused your document.
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