MySQL 1071: Specified key was too long (Laravel migration)

1. About the error
2. Why do I see this error
3. Solution
4. Recommended: set a default string length
5. Better long-term: upgrade MySQL
6. Per-column alternative

#About the error

Running php artisan migrate on a fresh install against older MySQL throws:

SQLSTATE[42000]: Syntax error or access violation: 1071
Specified key was too long; max key length is 767 bytes

It almost always fails on the users table when creating a unique index on the email or another VARCHAR(255) column.

#Why do I see this error

Laravel defaults to the utf8mb4 charset (proper 4-byte Unicode, needed for emoji and many scripts). In utf8mb4 each character can take up to 4 bytes, so a VARCHAR(255) index needs 255 × 4 = 1020 bytes.

On MySQL before 5.7.7 (and MariaDB before 10.2), the per-index limit without large-prefix support is 767 bytes, less than 1020, so the index creation fails.

#Solution

#Recommended: set a default string length

Laravel ships with a one-line fix. In app/Providers/AppServiceProvider.php, cap the default string length so indexed VARCHAR columns fit:

use Illuminate\Support\Facades\Schema;

public function boot(): void
{
    Schema::defaultStringLength(191);
}

191 × 4 = 764 bytes, just under the 767 limit. Then re-run the migration:

php artisan migrate:fresh

#Better long-term: upgrade MySQL

The 767-byte limit is a limitation of old versions. MySQL 5.7.7+ and 8.0 raise it to 3072 bytes with the InnoDB large prefix, and the error disappears without capping your column lengths. See upgrading MySQL 5.7 to 8.0 on Ubuntu.

#Per-column alternative

If you only need it on a specific migration, set the length on the column directly instead of globally:

$table->string('email', 191)->unique();