Free tools for web developers

CSS Gradient Generator Build linear, radial and conic gradients with draggable colour stops and copy clean CSS. htaccess Redirect Generator Generate single-hop HTTPS, www and bulk 301 redirects for Apache sites and migrations. Cron Expression Generator Turn schedules into cron expressions and check the next run times before deploying. JSON Formatter & Validator Format, validate and minify JSON with exact line and column errors, a collapsible tree view and sorted keys, all in the browser. Regex Tester Test JavaScript regular expressions with live highlighting, capture groups and a replace preview, safely sandboxed so a bad pattern cannot freeze the tab. Text Compare (Diff Checker) Compare two versions of a config file, template or copy side by side, with word-level highlighting inside changed lines. Colour Converter & Contrast Checker Convert HEX, RGB and HSL values and check WCAG 2.2 contrast before a colour goes into the design system. Redirect Checker Run every old URL from your redirect map through the checker before and after DNS cutover. It shows each hop and status code, so you catch 302s that should be 301s and ch... robots.txt Tester Staging sites usually carry a blanket Disallow. Test the live robots.txt on launch morning to confirm Googlebot and Bingbot can reach key templates and that the sitemap l... Security Headers Checker Check HSTS, CSP, X-Content-Type-Options, Referrer-Policy and framing controls on the production URL. Fixing missing headers before handover is far cheaper than explaining... Content Security Policy Generator Building a Content Security Policy by hand for a site with analytics, fonts and embedded video is fiddly. Generate a starting policy, deploy it in report-only mode, then... SSL Certificate Checker Confirm the certificate covers both the apex and www hostnames, the chain is complete and the expiry date is sensible. A missing intermediate certificate can work in desk... XML Sitemap Checker Validate the production sitemap after launch. It flags URLs that return redirects or errors, which is common when a CMS still lists staging paths or old slugs after a mig... Image Compressor Batch up to 20 client photos at once, set a max width and export as WebP for large savings. It runs in the browser, so unreleased product shots and client assets are neve... Favicon Generator Turn the client logo into favicon.ico, apple-touch-icon, the 192 and 512 PNGs and a site.webmanifest in one ZIP, with the HTML link tags ready to paste. It removes a smal... DNS Propagation Checker After changing A records or nameservers, check how the new values appear across resolvers before you tell the client the site is live. It helps explain why some staff sti... Email Deliverability Checker Run the client domain after any DNS move to confirm MX, SPF, DKIM and DMARC survived. Contact-form and order emails are the first thing clients notice when they stop. Broken Link Checker Crawl key pages for internal links that still point to staging, old slugs or deleted files. Fixing these before handover avoids soft 404s and a messy first Search Console... Website Down Checker Find out in seconds whether a website is down for everyone or only on your connection, and what kind of failure it is AI Content Visibility Checker Paste any page address to see whether AI search tools may fetch it, whether its text is in the HTML, and whether it is written so a passage can be quoted What Is My IP Address Your public IP address, the network it belongs to and what your browser shares with every site, plus a lookup for any IPv4 or IPv6 address Keyword Grouping Tool Paste a keyword list or upload a CSV export, and group it into topics you can plan one page around, with intent buckets and summed volume, impressions and clicks Bulk Redirect Checker Paste or upload up to 100 URLs and see where each one really ends: every hop with its status code, chains, loops and temporary redirects, plus a match check against the t... XML to JSON Converter Turn RSS feeds, sitemaps, SOAP responses and other XML into clean JSON, or build XML from JSON, with full control over how attributes, arrays and namespaces are mapped Color Palette Generator Build a palette from one color, pull the main colors out of an image, or press the space bar for random ideas Privacy Policy Generator Answer five short questions about your business, the data you collect and the tools you use, and get a starting-point privacy policy you can review, edit and publish WHOIS Lookup See the full public registration record for any domain: registrar and abuse contact, key dates, every status code in plain English, nameservers, DNSSEC and the raw record SSL Certificate & CSR Decoder Paste a PEM certificate, a full chain or a CSR to read every field in plain English, check that each certificate signs the next, and catch problems before you install it Subnet Calculator Enter any IPv4 or IPv6 address with a prefix or mask to get its network, host range, masks, address type and reverse DNS zone, then split it, plan VLSM subnets or summari... Image Alt Text Checker Paste a page address to list every image on it, see which have missing, empty or placeholder alt text, and find image links that screen readers cannot name HTTP Headers & Compression Checker Enter a URL to see every response header it sends, whether gzip or Brotli compression is on and how much it saves, and what its caching headers tell browsers and CDNs llms.txt Checker & Generator Enter a website to validate its llms Website Technology Checker Enter any website to find out which CMS, builder or store platform it runs on, the scripts and services it loads, and who hosts its website, DNS and email, with the evide... Subdomain Finder Enter a domain to list the subdomains recorded in public Certificate Transparency logs, check which ones still resolve, and flag forgotten records that could be taken ove... Color Contrast Checker Enter a text color and a background color to see their WCAG contrast ratio, whether they pass AA and AAA for normal and large text and for UI parts, and the closest shade... Mixed Content Checker Enter a page address to find every resource it still loads over plain http://, see which ones browsers block or upgrade, and check whether each file is already available...