I allowed more than one \d digit, with \d+.

It took me a while to grok it, but the original regex did allow more than one digit, and also captures it. That's because there is a \d in the character class, and the character class is quantified with a *. However this also allows more than one dot or more than one e, so it recognizes Ee.3 as a number.

I agree that your regex is much better to read, but it doesn't allowe numbers before the exponential (I guess that's what the e in the regex is supposed to mean).

Further refinements could use Regex::Common's number regex, or this regex, which parses numbers according to the JSON number specification:

my $number = qr{
    -?
    (?: 0 | [1-9] [0-9]* )
    (?: \. [0-9]+ )?
    (?: [eE] [+-]? [0-9] )?
}x;
[download]

(might be a bit too restrictive in some cases for parsing numbers "in the wild", but still a good inspiration).