What do the four flags tested here mean?

i = case-insensitive matching. g = global (find all matches, not just the first). m = multiline (^ and $ match start/end of each line, not just the whole string). s = dotAll (the . metacharacter also matches newline characters).

Why are there 16 combinations?

Each of the four flags can be either on or off, giving 2^4 = 16 possible combinations.

What happens if my pattern has a syntax error?

An error message is shown instead of results, and all cards display the error so you can fix the pattern before testing.

Does this tool send my pattern or text to a server?

No. All matching is done entirely in your browser using the built-in JavaScript RegExp engine. Nothing is transmitted anywhere.

Can I test other flags like u or v?

This tool focuses on the four most commonly misunderstood flags (i, g, m, s). Unicode (u/v) flags are not included to keep the comparison grid manageable.

Regex Flags Tester

Name: Regex Flags Tester
Availability: InStock
Author: Nham Vu

Enter a regex pattern and sample text to instantly see matches for every combination of i, g, m, and s flags side by side.

Regex Pattern (no slashes)

Test String

Multiline Test Text (optional — used instead of the field above when non-empty)

i = case-insensitive g = global (all matches) m = multiline (^ $ per line) s = dotAll (. matches newline)

Enter a pattern above to see results.

Summary

Enter a regex pattern and sample text to instantly see matches for every combination of i, g, m, and s flags side by side.

How it works

Enter your regex pattern in the pattern field (without slashes or flags).
Paste or type the test string you want to match against.
The tool evaluates your pattern against all 16 flag combinations automatically.
Each card shows the active flags, the number of matches, and the matched substrings highlighted.
Cards with at least one match are highlighted so you can spot them instantly.

Use cases

Understand how the i flag affects case-sensitive patterns.
Debug multiline patterns by comparing m flag on and off.
Check whether dotAll (s) is needed to match newlines with a dot.
Verify global (g) flag behavior versus single-match mode.
Quickly find the minimal set of flags needed for your use case.
Teach regex flag concepts visually in a classroom or code review.
Audit third-party patterns before integrating them into production code.
Confirm that your pattern does not over-match with certain flag combinations.

Frequently Asked Questions

Last updated: 2026-06-09 · Reviewed by Nham Vu