URL Decoder

How URL Decoding Works

URL decoding (percent decoding) is the reverse of the encoding process defined in RFC 3986 (Uniform Resource Identifier: Generic Syntax). When special characters appear in a URL, they are encoded as a percent sign followed by two hexadecimal digits representing the byte value. Decoding converts these percent-encoded sequences back to their original characters.

The Percent-Encoding Standard

RFC 3986 defines a set of unreserved characters that do not need encoding: A-Z a-z 0-9 - _ . ~. All other characters, including spaces, ampersands, equals signs, and non-ASCII Unicode characters, must be percent-encoded when used in URI components. For example, a space becomes %20, an ampersand becomes %26, and a Japanese character like a multi-byte UTF-8 sequence becomes multiple percent-encoded bytes (e.g., %E6%97%A5).

decodeURI vs decodeURIComponent

JavaScript provides two decoding functions. decodeURI() decodes a complete URI but preserves characters that have structural meaning in URLs: ; / ? : @ & = + $ , #. decodeURIComponent() decodes everything, including those reserved characters. Use decodeURIComponent() for query parameter values and path segments, and decodeURI() for full URIs where you want to keep the URL structure intact.

Common Use Cases

URL decoding is used when reading query parameters from analytics tools, processing redirect URLs in email campaigns, debugging encoded API request parameters, and extracting human-readable text from web server logs. This tool uses decodeURIComponent() for maximum compatibility with all percent-encoded content, including multi-byte UTF-8 sequences.