URL Encoding

URL encoding (percent-encoding) converts characters not allowed in URLs into %HH form, so arbitrary data can appear safely in URL components.

Purpose

It keeps reserved characters (such as /, ?, #, =) and non-ASCII characters from breaking URL structure, while remaining reversibly round-trippable.

Mechanism

Unsafe characters are converted byte-by-byte into % followed by two uppercase hexadecimal digits. RFC 3986 defines the reserved character sets; the HTML5 application/x-www-form-urlencoded form additionally encodes a space as +. Modern browsers and the fetch API handle this automatically.

Use cases

Passing non-ASCII text and special characters in URL query parameters
RESTful API path parameter encoding
OAuth callback URL encoding
Subject and body in mailto links

Examples

Input
```
a b&c
```
Output
```
a%20b%26c
```
RFC 3986 form; the form-encoded variant is a+b%26c

Common errors

Encoding the entire URL instead of just the parameter values: Encode parameter values only and keep the /?=& delimiters

Related terms

Percent-Encoding

Percent-encoding is the mechanism that converts unsafe characters in URLs into %HH form, defined by RFC 3986.

Form encoding (application/x-www-form-urlencoded) is how HTML forms encode key-value pairs on submission, encoding spaces as + instead of %20.

HTML entities escape characters with special meaning in HTML (<, >, &, ") into &name; or &#NNN; form so they display literally instead of being parsed as markup.

A URL (Uniform Resource Locator) is a string identifying the location of an Internet resource, comprising scheme, host, port, path, query, and fragment.

Related tools

Percent-encode text for safe use in URLs. Free, private, and 100% client-side.

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Parse a URL into its components: protocol, host, path, query, hash, port, username, and password. Free, private, and 100% client-side.

Url Encode Form

Url Encode Form — pure client-side tool. Privacy-first, no server round-trip.

Url Decode Form

Url Decode Form — pure client-side tool. Privacy-first, no server round-trip.

Url Decode Component

Url Decode Component — pure client-side tool. Privacy-first, no server round-trip.

Related tutorials

URL encoding: component vs full, and the reserved characters in between

Why encodeURIComponent and encodeURI produce different output, which characters are reserved in which position, and how to pick the right mode for query values, paths, and fragments.

References