Are regular expressions still not well implemented in the browser? In which failure: codepen
<form method="GET" name="formu" id="formu">
<p>
<input type="text" name="nombre" pattern="[A-Za-z]" required>
</p>
<button type="submit">Enviar</button>
</form> Try adding the symbol + , that is, telling the input field to accept one or more of the characters you have listed in the character class [] .
The pattern would look like this:
[A-Za-z]+
Example:
<form method="GET" name="formu" id="formu">
<p>
<input type="text" name="nombre" pattern="[A-Za-z]+" title="Solo admite letras A-Z y a-z" required>
</p>
<button type="submit">Enviar</button>
</form>