UTF-8 Validator + Sequence Inspector

Decode any byte sequence (entered as hex or text) and validate whether it's valid UTF-8. Flag malformed sequences, overlong encodings (security issue), and invalid surrogates. Shows the byte-by-byte breakdown with the resulting code points.

How to use the UTF-8 Validator + Sequence Inspector

Enter bytes as text (UTF-8 encoded) or as hex like 48 65 6c 6c 6f, pick the input mode, and the tool decodes them, flags any invalid sequences, and shows a byte-by-byte breakdown with the resulting code points.

Validating UTF-8 byte by byte

UTF-8 encodes each Unicode code point as one to four bytes following strict rules. Real-world data breaks those rules constantly — a file truncated mid-character, bytes from another encoding mislabeled as UTF-8, or deliberately malformed input such as overlong encodings, a classic trick for sneaking text past a naive filter.

This tool decodes a byte sequence (entered as text or hex) and checks whether it is valid UTF-8, flagging malformed sequences, overlong encodings, and invalid surrogate code points, then shows the byte-by-byte breakdown with each resulting code point. To inspect individual characters and their Unicode properties, use the Unicode inspector; to detect which encoding an uploaded file uses, the file encoding detector.

Common use cases

• Debugging mojibake — find the exact byte where a sequence stops being valid UTF-8.
• Security review — spot overlong encodings used to bypass input filters.
• API payloads — confirm a response body is well-formed UTF-8.
• Truncation checks — detect a string cut off in the middle of a multibyte character.
• Learning UTF-8 — see exactly how code points map to one, two, three, or four bytes.