UTF8MB3 to UTF8MB4 - MySQL Full Unicode Fix

Convert MySQL utf8/utf8mb3 to utf8mb4 for full emoji and Unicode support. Fix 4-byte character issues. Browser-based, private.

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MySQL UTF8 Limitation

MySQL's utf8 charset (utf8mb3) only supports 3-byte UTF-8 characters. Any character requiring 4 bytes—including all emoji—will cause "Incorrect string value" errors or data truncation.

Solution: Migrate to utf8mb4 which supports the full Unicode range. Use this tool to verify your data is utf8mb4 compatible and identify problematic characters.

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Frequently Asked Questions

MySQL's 'utf8' (now called utf8mb3) only supports 3-byte UTF-8 characters, excluding emoji and some rare CJK characters. UTF8MB4 supports the full 4-byte UTF-8 standard including all emoji, supplementary characters, and complete Unicode coverage.

MySQL's original utf8 was designed when 3 bytes seemed sufficient. When emoji and extended Unicode became common, MySQL couldn't change utf8 without breaking backward compatibility, so they created utf8mb4 as the true UTF-8 implementation.

UTF8MB3 cannot store: all emoji (😀 🎉 ❤️), supplementary CJK ideographs, mathematical symbols beyond basic set, musical symbols, ancient scripts, and any character requiring 4 bytes (Unicode code points above U+FFFF).

Run: SHOW CREATE TABLE your_table; Look for 'CHARACTER SET utf8' or 'utf8_general_ci'. In MySQL 8.0+, utf8 is aliased to utf8mb3 with deprecation warnings. Check collation with: SELECT @@character_set_database, @@collation_database;

MySQL returns 'Incorrect string value: \xF0\x9F...' errors, the insert fails completely, or (worse) the data is silently truncated at the emoji position. This corrupts user content and breaks user-generated content features.

Steps: 1) Backup database, 2) ALTER DATABASE db CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci, 3) ALTER TABLE each table, 4) Update my.cnf with character-set-server=utf8mb4, 5) Update application connection charset, 6) Test thoroughly.

Not for existing data—most characters still use 1-3 bytes. Storage increases only for 4-byte characters (emoji, rare symbols). Index size may increase since MySQL reserves 4 bytes per character for utf8mb4 columns in indexes.

In MySQL 5.6 with InnoDB, index keys are limited to 767 bytes. A utf8mb4 VARCHAR(191) is safe (191×4=764 bytes). In MySQL 5.7+ with innodb_large_prefix, you can use VARCHAR(255). Consider reducing column lengths or using prefix indexes.

Use utf8mb4_unicode_ci for proper Unicode sorting and comparison (more accurate for international text). Use utf8mb4_0900_ai_ci in MySQL 8.0+ for best performance. Avoid utf8mb4_general_ci except for legacy compatibility.

Downgrading from utf8mb4 to utf8mb3 will fail for any data containing 4-byte characters. Always backup before converting. If you have emoji in your data after upgrading, you cannot safely revert to utf8mb3.

MySQL UTF8 Limitation

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