There's also a ... newer version? at https://validator.w3.org/nu/ https://validator.w3.org/nu/ I'm not 100% sure what the difference is, but you can see the so

There's also a ... newer version? at https://validator.w3.org/nu/ https://validator.w3.org/nu/ I'm not 100% sure what the difference is, but you can see the source code at https://github.com/validator/validator https://github.com/validator/validator and report any issues.