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For people who build and run websites: make a favicon set, preview how a link will look when shared, check security headers and Content Security Policies, make SRI and CSP hashes, read and check structured data (JSON-LD, microdata and RDFa), test robots.txt rules, check and compare sitemaps, build redirect maps, parse user agents and look up HTTP status codes and MIME types.
Social Card PreviewPaste a page’s HTML to see how its link will look when shared on social sites and in chat apps, with missing or broken Open Graph and X card tags pointed out and a complete set to copy.
Structured Data ViewerPaste a page’s HTML, or JSON-LD on its own, to see every schema.org item in it as a tree, from JSON-LD, microdata and RDFa, with missing properties that Google’s rich results need pointed out, and the lot as JSON-LD to copy.
Favicon GeneratorTurn one picture into every icon a website needs: favicon.ico, Apple touch icon, Android and app icons including a maskable one, the web app manifest and the tags to paste into your pages, saved together as a ZIP.
Security Headers & CSPPaste a site’s response headers to have its security headers graded and explained, its Content Security Policy checked line by line, and its cookies’ flags checked. Build a new policy below.
SRI & CSP HashesDrop scripts and stylesheets to get their integrity attributes and the tags that load them, or paste HTML with inline scripts and styles to get the hashes a Content Security Policy needs to allow them. Paste an integrity value to check a file against it.
robots.txt TesterPaste a robots.txt and test whether a crawler may fetch each address, with the rule that decides it. Mistakes are pointed out, and so are the crawlers, AI ones included, that are blocked from the whole site.
Sitemap InspectorOpen or paste a sitemap.xml or sitemap index to list its entries and find mistakes: missing or repeated addresses, other hosts, badly written dates and values, and size limits. Add an earlier version to see what was added, removed or changed.
HTTP Codes & MIME TypesEvery HTTP status code with what it means, and the MIME type for common file extensions, searchable by number, name, word or extension.
User Agent ParserRead a User-Agent string: the browser and version, its engine, the operating system and the kind of device, with this browser's own string and client hints.
Redirect Map BuilderTurn a list of old and new addresses into redirect rules for Apache (.htaccess), nginx, Netlify or Cloudflare Pages, Vercel or Caddy, with duplicates, loops and chains found and chains pointed straight at their end.
CSS GradientMake a linear, radial or conic gradient from colour stops you type, see it as you go, and copy the CSS. Repeating gradients and mixing colours in oklch are options.
Box ShadowBuild a CSS box-shadow, or a text-shadow, from layers: offset, blur, spread, colour with transparency and inset. Add, remove and reorder layers, see the result and copy the CSS.
Clip-pathCut an element to a shape with CSS clip-path. Start from a triangle, chevron, star, circle, ellipse or inset, drag the points on the preview or move them with the arrow keys, and copy the CSS.
Easing CurveShape a CSS easing curve by dragging two handles, or choose a preset, bounce or steps, watch a ball move with it, and copy the cubic-bezier(), steps() or linear() value.
Blob ShapeMake a smooth, organic blob shape from a seed: the same seed always gives the same shape. Choose the number of points and how wobbly it is, then copy it as SVG or as a CSS clip-path.
Guides
Fixing sitemap errorsFind out why a search engine rejects or ignores your sitemap.xml: check it's well-formed XML, find bad addresses and dates, keep within the size limits, and make sure robots.txt lets crawlers reach it and the pages it lists.
Moving a website without losing visitorsRebuild or move a site without broken links: map every old address to its new one, turn the map into redirect rules for your server or host, avoid chains and loops, and check robots.txt, status codes, share previews and structured data on the new site.
Making a page look finished with CSSPick colours that match a logo and are readable, set a type scale, then build the gradient, shadow, shaped edge, blob and animation curve that make a plain page look finished.
Getting a website ready to launchThe finishing touches before a site goes live: favicons, share cards, structured data for search results, robots.txt and the sitemap, security headers and SRI hashes, and a check of its HTTPS certificate.
A website works for me but not for one userWhen a page works for you but not for someone else: find out their browser and settings, see what they see, capture the requests their browser makes, and check their keyboard, without a call or remote access.