UTF-8 explained

UTF-8 is how most of the web, Linux, and modern APIs store text. It encodes each Unicode character as one to four bytes. English letters look like ASCII; emoji and accented letters use more bytes. Our UTF-8 & Unicode tool shows the hex bytes for any string you type.

Unicode code points

Every character has a number — a code point. “A” is U+0041, “€” is U+20AC, “😀” is U+1F600. Programmers write them as U+ plus hex. Unicode defines the character; UTF-8 is one way to store that number in a file.

UTF-8 byte rules

• U+0000–U+007F (ASCII): one byte, same value as ASCII.
• U+0080–U+07FF: two bytes, leading 110xxxxx pattern.
• U+0800–U+FFFF: three bytes, leading 1110xxxx pattern.
• U+10000–U+10FFFF: four bytes, leading 11110xxx pattern.

Continuation bytes always start with 10xxxxxx. That lets parsers resync if a stream is damaged.

Worked examples

“A” (U+0041) → single byte 41.

“€” (U+20AC) → three bytes E2 82 AC.

“Hello” → five ASCII bytes; no multibyte characters.

Type any of these in the UTF-8 tool to see per-character breakdown and the full hex string.

Why UTF-8 won

UTF-8 is backward-compatible with ASCII, has no byte-order mark requirement, and avoids zero bytes in English text (helpful for C strings). UTF-16 is fixed-width for BMP characters but uses two or four bytes per code unit and needs endianness care. JSON, HTML, and Rust’s default String all assume UTF-8.

FAQs

What is BOM?

Byte order mark EF BB BF at the start of some UTF-8 files; UTF-8 does not need it for byte order.

Why does “length” differ in JavaScript?

string.length counts UTF-16 code units, not graphemes or UTF-8 bytes.

Is UTF-8 the same as Unicode?

Unicode is the character set; UTF-8 is an encoding of it. See also Number Base Conversions for hex and binary of byte values.

Sources

RFC 3629 (UTF-8); Unicode Standard; WHATWG encoding specification.