URL Encoder / Decoder

A URL Encoder/Decoder converts text to and from percent-encoding (also called URL encoding) — the mechanism defined in RFC 3986 that allows arbitrary characters to be safely included in URLs. URLs can only contain a limited set of ASCII characters; everything else must be encoded as one or more %XX sequences where XX is the character's hexadecimal byte value.

Why URL encoding exists

URLs were designed when the internet was primarily English-language text. The specification reserves certain characters for structural purposes: / separates path segments, ? starts the query string, & separates query parameters, = links parameter names to values, # starts a fragment. When any of these characters appear in the data of a URL parameter rather than as structural markers, they must be percent-encoded to prevent the URL parser from misinterpreting them.

For example, a search query like C++ programming cannot be passed as ?q=C++ programming in a URL because + has a special meaning (space in some contexts) and the space itself is invalid in a URL. Properly encoded: ?q=C%2B%2B%20programming.

Real-world encoding examples

Form submissions: HTML form data is URL-encoded before being sent to a server. Characters like &, =, and + in form field values are encoded so the server can unambiguously parse the parameter list.

API query parameters: Passing a date range like startDate=2024-01-01&endDate=2024-12-31 is straightforward, but passing a JSON object or array as a query parameter requires encoding the braces, quotes, and commas.

OAuth redirect URIs: OAuth 2.0 redirect_uri parameters must be URL-encoded because they contain ://, /, and ? characters that would otherwise be interpreted as part of the outer URL structure.

International characters (IDN): Non-ASCII characters in URLs — like Nepali (नेपाली) or Arabic script in a query string — are UTF-8 encoded first, then percent-encoded.

Debugging API calls: When a fetch() call or HTTP request fails, URL-decoding the request URL in browser DevTools or server logs reveals the actual parameter values being sent, which often explains unexpected API behaviour.

Encoding vs decoding

Encoding converts raw text to percent-encoded form. Decoding converts percent-encoded form back to readable text. Both are essential: encode when constructing URLs, decode when reading them from logs, analytics, or server-side request objects. The UtilsGo URL Encoder/Decoder processes everything in your browser with no data transmitted externally.