Network/HTTP
Generate or decode an HTTP Basic Authentication header — Base64(username:password).
Break a URL down into its parts — protocol, host, port, path, query parameters, fragment.
Parse a URL query string into a JSON object, or build a query string back from JSON.
Break a User-Agent string down into browser, engine, operating system, and device type.
Parse raw HTTP headers (from curl -I, DevTools, raw response) into a field list with descriptions and a security headers check.
Parse a Set-Cookie header or a Cookie/document.cookie string into name, value, attributes, and a check for common security mistakes.
Explain step by step whether the browser will allow a cross-origin request — simple/preflight classification, Access-Control-* response header checks, and a verdict.
Encode and decode HTML entities — safely display special characters on a page.
Compress HTML for production, or format minified markup into a readable layout.
Exact age from a birth date — years/months/days, total time lived, and the next birthday.
Convert colors between HEX, RGB, HSL, HSV/HSB, and CMYK — enter a value into any field and the rest update instantly.
Convert line endings between Windows (CRLF), Unix/macOS (LF), and classic Mac (CR), with mixed-ending detection.
Build a sitemap.xml from a list of URLs — with lastmod/changefreq/priority, validation, and duplicate removal.