Test regex flags

Test a JavaScript regular expression while seeing how each selected flag changes matching.

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ToolRegex Flags Tester
Input
Output
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Preview

How it works

The expression is compiled with selected flags; case folding, multiline anchors, dot matching, Unicode handling, and global iteration then affect the result. Invalid flag combinations are reported before matching.

  • JavaScript’s standard flags are exposed individually.
  • Global mode changes repeated-match state.

Worked example

Compare case-sensitive vs case-insensitive matching
Compare how different flags affect matching of mixed-case text
Input
											Hello hello HELLO world
Output
												Pattern: /hello/
Test string: "Hello hello HELLO world"

Flag      Description                                  Matches
-----------------------------------------------------------------
(none)    (no flags)                                   1
g         g - global                                   1
i         i - case insensitive                         1
m         m - multiline                                1
s         s - dotAll                                   1
gi        gi - global + case insensitive               3
gm        gm - global + multiline                      1
gim       gim - global + case insensitive + multiline  3
gims      gims - all common flags                      3…

When to use this

Frontend validation, regex teaching, and pattern debugging test flags.

Edge cases

  • g advances lastIndex between tests.
  • m makes anchors match line boundaries inside multiline text.
  • i folds case but does not normalize arbitrary Unicode characters.

References