Regular Expressions 101

^start of line

Non-Capturing Group(?:(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)\.){3}

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

Non-Capturing Group(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)

1st Alternative25[0-5]

25the literal text 25

Character Class[0-5]

0-5one character from 0 (48₁₀) to 5 (53₁₀)

2nd Alternative2[0-4]\d

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Character Class[0-4]

0-4one character from 0 (48₁₀) to 4 (52₁₀)

\da digit

3rd Alternative1\d\d

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

\da digit

4th Alternative[1-9]\d

Character Class[1-9]

1-9one character from 1 (49₁₀) to 9 (57₁₀)

\da digit

5th Alternative\d

\da digit

\.the literal . (46₁₀ / 56₈ / 2E₁₆)

Non-Capturing Group(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)

1st Alternative25[0-5]

25the literal text 25

Character Class[0-5]

0-5one character from 0 (48₁₀) to 5 (53₁₀)

2nd Alternative2[0-4]\d

2the literal 2 (50₁₀ / 62₈ / 32₁₆)

Character Class[0-4]

0-4one character from 0 (48₁₀) to 4 (52₁₀)

\da digit

3rd Alternative1\d\d

1the literal 1 (49₁₀ / 61₈ / 31₁₆)

\da digit

4th Alternative[1-9]\d

Character Class[1-9]

1-9one character from 1 (49₁₀) to 9 (57₁₀)

\da digit

5th Alternative\d

\da digit

$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

Regular Expression

^(?:(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)$

New

// Accept ✅
127.0.0.1
192.168.1.1
192.168.1.255
255.255.255.255
0.0.0.0

// Reject ❌
033.33.33.33
127.1
192.168.1.256
-1.2.3.4
1.1.1.1.