// character encoding

What Is UTF-8?

UTF-8 is a character encoding used to represent text inside computers. It provides a way of turning Unicode characters such as letters, numbers, mathematical symbols and characters from many languages into bytes that a computer can store and process.

// definition

UTF-8 turns characters into bytes

UTF-8 stands for Unicode Transformation Format - 8-bit.

It is an encoding system that converts Unicode characters into sequences of bytes.

This allows text to be stored in files, transmitted across networks and interpreted consistently by different computer systems.

// why encoding?

Computers do not store letters directly

When we look at a computer screen, we see characters:

A £ π é 日 😀

But computer storage ultimately consists of binary data. The computer therefore needs a defined system for representing each character using numbers and bytes.

Character → Unicode code point → UTF-8 encoding → Bytes

// unicode

First, understand Unicode

Unicode is a standard that assigns characters unique numerical identifiers called code points.

A Unicode code point is normally written using U+ followed by hexadecimal digits.

Character	Unicode code point
A	U+0041
£	U+00A3
é	U+00E9
π	U+03C0
€	U+20AC
😀	U+1F600

// unicode vs utf-8

Unicode and UTF-8 are not the same thing

This distinction is important.

Unicode

Defines characters and assigns them code points.

UTF-8

Defines how those Unicode code points are encoded into bytes.

Unicode tells us that the pound sign is U+00A3. UTF-8 tells the computer which bytes should be used to represent that character.

// bytes

UTF-8 uses between one and four bytes

UTF-8 is a variable-length encoding.

Different characters require different numbers of bytes.

Character	UTF-8 bytes	Bytes used
A	41	1
£	C2 A3	2
π	CF 80	2
€	E2 82 AC	3
😀	F0 9F 98 80	4

Important: the hexadecimal byte values shown above are the UTF-8 encoding of each character, not the Unicode code point itself.

// ascii compatibility

UTF-8 is compatible with ASCII

One of the reasons UTF-8 became so successful is its compatibility with ASCII.

The first 128 Unicode characters use exactly the same single-byte values as ASCII.

A = U+0041 = UTF-8 byte 41 B = U+0042 = UTF-8 byte 42 1 = U+0031 = UTF-8 byte 31

This means ordinary English text using basic letters, digits and punctuation is very compact in UTF-8.

// multilingual text

UTF-8 can represent text from many languages

UTF-8 is not limited to English.

English: Hello Português: Olá Español: Información Français: Éducation Greek: π Japanese: 日本 Currency: £ € ¥ Mathematics: ≤ ≥ ± √ ∞ Emoji: 😀

All of these characters can exist within the same UTF-8 encoded document.

// encoding errors

What happens when the wrong encoding is used?

Text can become corrupted-looking when software interprets bytes using the wrong character encoding.

For example, a pound sign encoded as UTF-8 may sometimes incorrectly appear as:

Expected: £50 Incorrect interpretation: Â£50

This type of garbled text is often called mojibake.

The data may not actually be damaged. The same bytes may simply have been interpreted using the wrong encoding.

// txt files

UTF-8 and .txt files

A .txt file tells us that a file contains plain text, but it does not automatically tell us which character encoding was used.

.txt ≠ automatically UTF-8

A text file might use UTF-8, ASCII, Windows-1252 or another encoding.

For modern text files, UTF-8 is generally the most useful and interoperable choice.

// csv files

UTF-8 and CSV

CSV is also a text-based format, so character encoding matters.

Name,City,Amount João,Lisboa,£50 Élodie,Paris,€75 Sofia,Athens,€40

Saving this file using UTF-8 helps preserve accented characters and currency symbols when the file moves between compatible systems.

// xml

UTF-8 and XML

XML documents can explicitly declare their character encoding.

<?xml version="1.0" encoding="UTF-8"?>

This tells the software reading the document that its characters are encoded using UTF-8.

// html

UTF-8 on websites

Websites also need to specify how text should be interpreted.

Modern HTML pages commonly include:

This tells the browser to interpret the document using UTF-8.

Correct encoding is important for displaying names, symbols, mathematical notation, international text and other characters reliably.

// advantages

Why is UTF-8 so widely used?

Unicode support

It can represent the full range of Unicode code points.

ASCII compatible

Basic ASCII characters retain their original one-byte representation.

Efficient

Common English characters require only one byte, while additional bytes are used when necessary.

Portable

UTF-8 is supported across operating systems, programming languages, databases and web technology.

// where it appears

UTF-8 appears throughout modern computing

UTF-8 can be used with many text-based technologies and file formats.

TXT CSV XML JSON HTML CSS JavaScript APIs Databases Web Pages

// key idea

The file format and the encoding are different things

This is one of the most useful concepts to understand.

File format: describes how information is organised.

Character encoding: describes how the characters themselves are represented as bytes.

CSV = structure of the data UTF-8 = encoding of the characters

A CSV file can therefore be encoded using UTF-8. An XML document can be encoded using UTF-8. A plain .txt file can also be encoded using UTF-8.

// summary

Characters become bytes.

UTF-8 is a character encoding that converts Unicode characters into sequences of one to four bytes. It allows computers to store and exchange text from many languages, symbols and writing systems while remaining compatible with ASCII.

// file formats

What Is a .txt File?

A .txt file is one of the simplest ways of storing information on a computer. It contains plain text without the complex formatting found in documents, spreadsheets or web pages.

// definition

Plain text, stored in a file

A .txt file is a plain-text file. The letters .txt are the file extension, which tells a computer that the file primarily contains text.

Unlike a Microsoft Word document, a .txt file does not normally contain information about fonts, colours, page layouts, images or complex formatting.

It is essentially a sequence of characters stored in a file.

// example

What does a .txt file contain?

A text file might contain something as simple as:

> Customer: Jane Smith Order Number: 10452 Product: Laptop Stand Quantity: 2 Status: Dispatched

There is no special document structure required here. These are simply characters and line breaks stored inside a file.

// why use txt?

Simple files can be extremely useful

Lightweight

Text files usually require very little storage because they contain little more than the characters themselves.

Widely supported

Almost every operating system and programming language can read and write plain-text files.

Easy to inspect

A person can open a .txt file directly and see the information without needing specialist software.

Easy to process

Programs and scripts can search, transform and analyse text files very efficiently.

// data

A .txt file can contain many kinds of information

The .txt extension does not dictate exactly what the text must represent.

A text file could contain notes, lists, configuration information, source data, logs, mathematical expressions, website content or information intended to be processed by another program.

Notes Lists Logs Data Code Configuration URLs Mathematics

// encoding

What does UTF-8 have to do with .txt files?

Computers ultimately store information as numbers. A text encoding defines how those numbers correspond to characters such as letters, numbers and symbols.

UTF-8 is one of the most widely used character encodings. It can represent ordinary English text as well as characters from a huge range of languages and writing systems.

> English Português Mathematics: π ≈ 3.14159 Currency: £50 Symbols: ≤ ≥ ± √

Important: a file ending in .txt is not automatically guaranteed to use UTF-8. Text files can use different character encodings.

When exchanging modern text data, UTF-8 is usually an excellent choice because it supports such a wide range of characters.

// txt vs document

A text file is not the same as a formatted document

Suppose you write:

Hello, world!

A .txt file mainly stores those characters.

A word-processing document may also store information describing the font, font size, colour, margins, paragraph spacing, images and many other formatting properties.

This is why plain-text files are often much simpler to process programmatically.

// related formats

Many important file formats are text-based

Plain text is also the foundation of many structured formats used throughout computing and the web.

.txt .csv .json .xml .html .css .js

These formats add their own rules and structures, but the underlying content can still be represented as text.

This is one reason understanding plain text is so useful when working with data, websites, APIs and automation.

// practical use

When is a .txt file useful?

Saving simple information

Notes, instructions, lists or other information that does not require visual formatting.

Moving data

Text can be transferred between different applications and computer systems with relatively little complexity.

Programming

Scripts can create, read, search and modify text files easily.

Automation

Text files can act as simple inputs, outputs, logs or intermediate data in automated processes.