URL Builder & Query String Parser

Build mode: enter a base URL and key/value pairs to get a properly percent-encoded URL. Parse mode: paste a URL to split it into protocol, host, path, query params, and hash.

How it works

Both directions use the browser's native URL and URLSearchParams APIs, so query parameter values are percent-encoded (or decoded) exactly the way a real browser or HTTP client would handle them — spaces become +, reserved characters become %XX sequences, and existing query parameters on the base URL are preserved rather than overwritten. A parameter row with an empty key is skipped, so it never produces a stray ?=value in the output.