UTF-8 Encoder and Decoder

What this UTF-8 tool does

This tool works in two directions. Encode mode turns Unicode text into UTF-8 bytes and formats those bytes as hexadecimal, decimal, binary, 0x-prefixed, or \x-prefixed values. Decode mode parses a selected byte representation, validates the bytes as strict UTF-8, and returns Unicode text. The page runs locally in your browser.

The byte layer is explicit. A JavaScript string is not a byte array, and a byte dump is not automatically text. This page keeps those steps separate so malformed byte syntax, malformed UTF-8, optional BOM handling, and Unicode normalization can be diagnosed without guessing.

Unicode vs UTF-8

Unicode defines abstract code points such as U+0041, U+00E9, and U+1F600. UTF-8 is one way to encode those code points as bytes. ASCII code points use one byte, many Latin, Greek, and Cyrillic characters use two, many CJK characters and symbols use three, and supplementary characters such as many emoji use four.

That means character counts and byte counts are different questions. é is one Unicode code point but two UTF-8 bytes. 😀 is one code point but four UTF-8 bytes. A grapheme cluster such as a family emoji or a combining sequence may contain several code points and therefore many bytes.

How many bytes UTF-8 uses

UTF-8 examples

Valid and invalid UTF-8

UTF-8 uses leading bytes and continuation bytes. A continuation byte is in the range 80 through BF. Invalid data can contain a leading byte without enough continuations, a continuation byte where a leading byte is required, an overlong encoding, a surrogate-range encoding, or a four-byte sequence above U+10FFFF. Decode mode reports byte offsets using one-based positions.

Examples such as C3, C3 28, A0 A1, ED A0 80, and F4 90 80 80 are rejected in UTF-8 text mode. Byte inspection mode still shows the parsed bytes when byte syntax is valid but the bytes are not text.

Supported byte formats

48 65 6C
48656C
72 101 108
01001000 01100101
0x48 0x65
\x48\x65

Auto-detect accepts clear input and reports ambiguity when the same text could mean more than one byte format. Choose the format explicitly for copied byte dumps, especially when values contain only digits.

UTF-8 BOM

The UTF-8 BOM is the byte sequence EF BB BF. It is optional in UTF-8 and is not normally required. Encode mode can add it only when you select that option. Decode mode can report and preserve a leading U+FEFF, remove it, or reject it. The same bytes in the middle of input are treated as text data, not as a BOM.

Unicode normalization

Normalization is separate from UTF-8 validity. With normalization off, é encodes as C3 A9, while e plus U+0301 encodes as 65 CC 81. If you choose NFC before encoding, the decomposed sequence may become the precomposed character and produce different bytes.

Binary data vs UTF-8 text

Valid byte syntax may represent images, PDFs, ZIP data, protocol messages, or text in another encoding. That data can be useful but not valid UTF-8. Use byte inspection when you need to inspect bytes without interpreting them as Unicode text.

How to use the tool

1. Choose Encode or Decode.
2. For Encode, enter text and choose an output byte format, separator, casing, normalization, and optional BOM.
3. For Decode, paste bytes, choose the byte input format, output mode, and BOM behavior.
4. Use Auto-detect only for clear byte formats; choose explicitly when the page reports ambiguity.
5. Review statistics, warnings, and diagnostics before copying or downloading.

Privacy and processing

This tool runs in your browser. Your input is not submitted to UnicodeNow. The output is written as textarea text, and downloads use Blob URLs that are revoked after use.

Common uses

• Inspecting UTF-8 bytes.
• Validating API payloads.
• Debugging malformed text.
• Testing emoji encoding.
• Comparing normalization forms.
• Checking BOM behavior.
• Reviewing copied byte dumps.

Example

Input text:

Hello, café 😀

UTF-8 hex:

48 65 6C 6C 6F 2C 20 63 61 66 C3 A9 20 F0 9F 98 80

UTF-8 bytes:

48 65 6C 6C 6F

Decoded text:

Hello

Frequently asked questions