Regular Expression Tester

Test a JavaScript pattern against sample text

A regular expression (regex) describes a text pattern: for example, \d{4}-\d{2}-\d{2} looks for four digits, a hyphen, two digits, another hyphen, then two digits. Enter the pattern by itself in the pattern field and put options such as g or i in the separate flags field. The tester applies the current browser’s JavaScript regular-expression rules as you edit the pattern, flags, or sample. It shows matched text or a syntax error.

The starting flags are gm: global search looks for multiple matches, and multiline mode changes how ^ and $ treat line boundaries. The results are the values returned by JavaScript string matching, so the flag choice affects both how much text is found and what appears in the list.

Why the g flag changes the result

With g, the list contains successive full matches. Without it, matching stops at the first occurrence; if the pattern contains capturing parentheses, the returned list can also contain the captured parts. For instance, testing ([A-Z]+)-(\d+) against AB-12 CD-34 with g returns the two full strings. Without g, the first full match and its captured pieces may appear. The count is the number of listed values, not always the number of match positions.

Other familiar flags include i for case-insensitive matching, m for line-aware anchors, and s to let a dot match a line break. The pattern syntax and accepted flags are those supported by the browser’s JavaScript engine.

Build a useful test case

1. Use representative text

   Include examples that should match and near-misses that should not. A pattern that passes one ideal example may still be too broad or too narrow on real input.

2. Enter the pattern and flags separately

   For a date-shaped string, enter \d{4}-\d{2}-\d{2}, without surrounding slash marks. Leave g enabled to see repeated matches; add or remove one flag at a time to isolate a change.

3. Read and copy the output

   Review each listed value and the match count. The copy control places the listed values on separate lines. If the result is empty, check the spelling, escaping, flags, and whether the sample contains the expected characters.

To extract order codes from Order A-102; Order B-305, try [A-Z]-\d{3} with g. You should see A-102 and B-305.

Common regex tester questions

Check the target engine before relying on a pattern

• This page tests JavaScript regex behavior. Python, Java, databases, editors, and other runtimes may use different syntax or options; rerun the pattern where it will actually run.
• A match means the text fits the pattern, not that an email address exists, a date is valid on a calendar, or a value meets your business rules. The included presets are starting patterns, not verification services.
• Patterns with costly backtracking can make interactive testing sluggish. Start with a small sample and simplify a pattern that causes long pauses.
• Do not use a shape check as a substitute for validating important data at the point where it is accepted.