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.
- JSON format & minify
Validate, pretty-print, or compress JSON for configs and APIs.
In-browser PerformanceSecurityOpen - Unix time converter
Parse ISO strings or Unix seconds/ms into local time and UTC.
In-browser PerformanceOpen - UUID generator
Random UUID v4 values for fixtures, IDs, and placeholders.
In-browser PerformanceSecurityOpen
Hand-picked from the web
Editorial bookmarks for audits and research — each opens in a new tab at the provider.
- Bundlephobia
Check npm package size and dependency cost before you install.
PerformanceExternal - Can I use
Browser support tables for HTML, CSS, and JavaScript features.
PerformanceSEOExternal - Chrome DevTools
Performance panel, coverage, and memory tooling in the browser.
PerformanceExternal - GTmetrix
Performance scores, waterfalls, and historical monitoring for a URL.
PerformanceExternal - PageSpeed Insights
Lab + field data from Lighthouse for any public URL.
PerformanceExternal - 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 - WebPageTest
Filmstrip, waterfalls, and multi-location runs.
PerformanceExternal
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.