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---
title: "UTF-8 - Glossary | MDN"
chunk: 1/3
source: "https://developer.mozilla.org/en-US/docs/Glossary/UTF-8"
category: "reference"
tags: "web, html, css, javascript, documentation"
date_saved: "2026-05-05T05:48:02.195471+00:00"
instance: "kb-cron"
---
* [Skip to main content](https://developer.mozilla.org/en-US/docs/Glossary/UTF-8#content)
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1. [Glossary](https://developer.mozilla.org/en-US/docs/Glossary)
2. [UTF-8](https://developer.mozilla.org/en-US/docs/Glossary/UTF-8)
# UTF-8
UTF-8 (UCS Transformation Format 8) is the World Wide Web's most common [character encoding](https://developer.mozilla.org/en-US/docs/Glossary/Character_encoding). Each character is represented by one to four bytes. UTF-8 is backward-compatible with [ASCII](https://developer.mozilla.org/en-US/docs/Glossary/ASCII) and can represent any standard Unicode character.
The first 128 UTF-8 characters precisely match the first 128 ASCII characters (numbered 0-127), meaning that existing ASCII text is already valid UTF-8. All other characters use two to four bytes. Each byte has some bits reserved for encoding purposes. Since non-ASCII characters require more than one byte for storage, they run the risk of being corrupted if the bytes are separated and not recombined.
## In this article
* [See also](https://developer.mozilla.org/en-US/docs/Glossary/UTF-8#see_also)
## [See also](https://developer.mozilla.org/en-US/docs/Glossary/UTF-8#see_also)
* [UTF-8](https://en.wikipedia.org/wiki/UTF-8) on Wikipedia
* [FAQ about UTF-8 on Unicode website](https://www.unicode.org/faq/utf_bom.html#UTF8)
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