UTF-8 Validator: Check and Validate UTF-8 Encoding

Validate UTF-8 encoded text and detect common encoding errors. Analyzes byte sequences, identifies invalid characters, and shows code point details. Essential for debugging character encoding problems in web applications and data processing.

Input Mode

Text to Validate

UTF-8 Encoding Rules

UTF-8 is a variable-length character encoding that uses 1-4 bytes per character.

1 byte (ASCII):

0xxxxxxx (0-127)

2 bytes:

110xxxxx 10xxxxxx

3 bytes:

1110xxxx 10xxxxxx 10xxxxxx

4 bytes:

11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

Continuation bytes always start with 10xxxxxx
Overlong encodings are invalid
Code points U+D800-U+DFFF (surrogates) are invalid

How it works

This tool validates whether text or byte sequences form valid UTF-8 encoded data. UTF-8 has strict rules about which byte sequences are legal, and this validator checks each byte against those rules.

UTF-8 uses 1-4 bytes per character. Single-byte characters (0-127) are ASCII. Multi-byte sequences must follow specific patterns: continuation bytes must start with 10xxxxxx, and the total length must match the leading byte's indication.

UTF-8 byte patterns:

0xxxxxxx1-byte character (ASCII)

110xxxxx 10xxxxxx2-byte character

1110xxxx 10xxxxxx 10xxxxxx3-byte character

Paste text or hex bytes to validate. The tool highlights invalid sequences and explains what went wrong—missing continuation bytes, overlong encoding, or invalid code points.

When you'd actually use this

Debugging character encoding corruption

A developer sees garbled text in logs and suspects encoding issues. They validate the byte sequence to find where invalid UTF-8 starts, pinpointing where data got corrupted in the pipeline.

Testing file upload validation

A backend engineer builds an API that accepts text files. They test with invalid UTF-8 sequences to ensure the validator rejects malformed input before it causes database issues.

Analyzing network packet captures

A security analyst examines HTTP traffic and needs to verify whether payload data is valid UTF-8. Invalid sequences might indicate encoding attacks or data exfiltration attempts.

Fixing database encoding errors

A DBA encounters "invalid byte sequence for UTF-8" errors during import. They validate the source file to identify problematic bytes before cleaning and re-importing.

Building robust text parsers

A developer writes a parser that must handle potentially malformed input. They use this validator to test edge cases and ensure their error handling covers all invalid UTF-8 patterns.

Forensic analysis of corrupted files

A forensic examiner recovers text from damaged storage. They validate UTF-8 sequences to separate recoverable text from corrupted regions that need reconstruction.

What to know before using it

Valid UTF-8 isn't always valid text.A sequence can be valid UTF-8 but represent nonsense characters or unassigned code points. This validator checks encoding rules, not semantic meaning.

Overlong encodings are invalid.Encoding ASCII 'A' (0x41) as a 2-byte sequence is technically decodable but violates UTF-8 rules. This validator catches overlong encodings that some decoders might accept.

Surrogate codes are forbidden in UTF-8.Code points U+D800 to U+DFFF are reserved for UTF-16 surrogates and must not appear in valid UTF-8. This validator rejects them.

Truncated sequences are common errors.A 3-byte character cut off after 2 bytes is invalid. This happens when files are truncated or strings are cut at byte boundaries instead of character boundaries.

Security note: Invalid UTF-8 can bypass security filters that assume valid encoding. Always validate input before processing, especially for paths, URLs, and database queries.

Common questions

What makes UTF-8 invalid?

Common issues: continuation bytes without a leading byte, wrong number of continuation bytes, overlong encodings, surrogate code points, or bytes above 0xF4. Any of these make UTF-8 invalid.

How do I fix invalid UTF-8?

Options: remove invalid bytes, replace with replacement character (U+FFFD), or re-encode from the original source if available. The right fix depends on your use case and data importance.

Can ASCII be invalid UTF-8?

No, pure ASCII (bytes 0-127) is always valid UTF-8. UTF-8 was designed to be backward compatible with ASCII. Invalid UTF-8 always involves bytes 128-255.

What's the replacement character?

U+FFFD () is the Unicode replacement character. It marks where invalid or unrepresentable characters were encountered. Many systems use it to replace invalid UTF-8 sequences.

Why do I see instead of text?

The diamond-question mark indicates invalid or unrenderable characters. Your system encountered bytes that aren't valid UTF-8 or characters your font can't display.

Is UTF-8 the same as ASCII?

ASCII is a subset of UTF-8. Bytes 0-127 mean the same thing in both. UTF-8 extends ASCII to support all Unicode characters using multi-byte sequences.

How do I prevent UTF-8 errors?

Always declare UTF-8 encoding (in HTML meta tags, HTTP headers, database connections). Validate input at system boundaries. Use libraries that handle UTF-8 correctly.

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