Regular Expressions 101

Pro

Positive Lookahead(?=^(?!(?:\w*(.)\1){3}).+$)

^start of line

Negative Lookahead(?!(?:\w*(.)\1){3})

Non-Capturing Group(?:\w*(.)\1){3}

{3}repeats the group contents below exactly 3 times:

\w*any word character, repeated any number of times

Group 1(.)

.any character (except for line terminators)

\1the text saved by group 1

.+any character (except for line terminators), repeated at least once

$end of line

Positive Lookahead(?=^(?:(.)(?!(?:.*?\2){4}))*$)

^start of line

Non-Capturing Group(?:(.)(?!(?:.*?\2){4}))*

*repeats the group contents below any number of times:

Group 2(.)

.any character (except for line terminators)

Negative Lookahead(?!(?:.*?\2){4})

Non-Capturing Group(?:.*?\2){4}

{4}repeats the group contents below exactly 4 times:

.*?any character (except for line terminators), repeated any number of times

\2the text saved by group 2

$end of line

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Detailed match information will be displayed here automatically.

25 tokens

(?=^(?!(?:\w*(.)\1){3}).+$)(?=^(?:(.)(?!(?:.*?\2){4}))*$)

New

adminnisstrator21
kkeeykloakk
stack22ooverflow
blahbllahhblaafaa

test$$$$test
test$$$$$test
testttest
adcdddd

adminnisstrator21
kkeeykloakk
stack22ooverflow
blahbllahhblaafaa

test$$$$test
test$$$$$test
testttest
adcdddd