Curated picks
Tools
Open a card for a full guide and a browser-only tool — no uploads. Details and external picks are below.
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In-browser tools
Utilities that run locally in your browser — use the topic filter above to narrow the list.
Hand-picked from the web
Editorial bookmarks for audits and research — each opens in a new tab at the provider.
- Security Headers
Quick report on HSTS, CSP, and related response headers.
SecurityExternal - Squoosh
Compress and convert images in the browser before you ship them.
PerformanceExternal - W3C CSS Validator
Check CSS for errors and warnings.
PerformanceSEOExternal - W3C Markup Validator
Validate HTML documents for syntax and parse errors.
PerformanceSEOExternal - WAVE
Visual feedback on structure, contrast, and ARIA on live pages.
AccessibilityExternal - WebAIM Contrast Checker
Check foreground/background contrast ratios against WCAG levels.
AccessibilityExternal - WebPageTest
Filmstrip, waterfalls, and multi-location runs.
PerformanceExternal - Website Carbon Calculator
Rough CO₂ estimate per page view and hosting context.
EcologyExternal
Further down you will find hand-picked third-party tools we use in audits (each opens in a new tab), plus links to our topic hubs and the rest of the site.
For deeper reading, jump into our topic hubs. Everything here opens in a new tab on the provider’s site.
Explore our Performance, Ecology, Accessibility, Security, and SEO hubs for deeper reading.