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---
title: "Percent-encoding - Glossary | MDN"
chunk: 1/3
source: "https://developer.mozilla.org/en-US/docs/Glossary/Percent-encoding"
category: "reference"
tags: "web, html, css, javascript, documentation"
date_saved: "2026-05-05T05:40:13.513580+00:00"
instance: "kb-cron"
---
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1. [Glossary](https://developer.mozilla.org/en-US/docs/Glossary)
2. [Percent-encoding](https://developer.mozilla.org/en-US/docs/Glossary/Percent-encoding)
# Percent-encoding
**Percent-encoding** is a mechanism to encode 8-bit characters that have specific meaning in the context of [URLs](https://developer.mozilla.org/en-US/docs/Glossary/URL). It is sometimes called URL encoding. The encoding consists of a substitution: A '%' followed by the hexadecimal representation of the ASCII value of the replaced character.
Special characters needing encoding are: `':'`, `'/'`, `'?'`, `'#'`, `'['`, `']'`, `'@'`, `'!'`, `'$'`, `'&'`, `"'"`, `'('`, `')'`, `'*'`, `'+'`, `','`, `';'`, `'='`, as well as `'%'` itself. Other characters don't need to be encoded, though they could.
| Character | Encoding |
| --- | --- |
| `':'` | `%3A` |
| `'/'` | `%2F` |
| `'?'` | `%3F` |
| `'#'` | `%23` |
| `'['` | `%5B` |
| `']'` | `%5D` |
| `'@'` | `%40` |
| `'!'` | `%21` |
| `'$'` | `%24` |
| `'&'` | `%26` |
| `"'"` | `%27` |
| `'('` | `%28` |
| `')'` | `%29` |
| `'*'` | `%2A` |
| `'+'` | `%2B` |
| `','` | `%2C` |
| `';'` | `%3B` |
| `'='` | `%3D` |
| `'%'` | `%25` |
| `' '` | `%20` or `+` |
Depending on the context, the character `' '` is translated to a `'+'` (like in the percent-encoding version used in an `application/x-www-form-urlencoded` message), or in `'%20'` like on URLs.
## In this article
* [See also](https://developer.mozilla.org/en-US/docs/Glossary/Percent-encoding#see_also)
## [See also](https://developer.mozilla.org/en-US/docs/Glossary/Percent-encoding#see_also)
* Definition of [percent-encoding](https://en.wikipedia.org/wiki/Percent-encoding) in Wikipedia.
* [RFC 3986](https://datatracker.ietf.org/doc/html/rfc3986), section 2.1, where this encoding is defined.
* [`encodeURI()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURI) and [`encodeURIComponent()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/encodeURIComponent) — functions to percent-encode URLs
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