Network/HTTP
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.
Generate or decode an HTTP Basic Authentication header — Base64(username:password).
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.
Fix broken JSON — trailing commas, single quotes, unquoted keys, comments, Python literals (True/False/None), and more — with a full list of every fix applied.
Encode text (Latin and Cyrillic) into Morse code (dots and dashes) and back. Characters without a table entry are skipped.
Hash passwords with Argon2 (winner of the Password Hashing Competition, RFC 9106) — d/i/id variants, with verification against an existing hash.
Find the ISO 8601 week number for a date, or find the start/end dates of a specific week.
Convert a number into text (in Ukrainian, Russian, or English), with an optional currency-amount mode for hryvnia, dollar, euro, or ruble.