SnapTool Logo
SnapToolSnap. Solve. Done.

Regex Tester & Explainer

Compile, test, and debug regular expressions online. View live highlighted matching strings, inspect capture groups, and understand flag parameters.

Last Updated: May 2026

Regular Expression Pattern

//gi
Hello 2026, this is SnapTool version 42!

No Matches Found

Ensure your regex pattern is correct and active flags capture matches inside your test string.

Regex Flag Explanations

Global Match (/g)Instructs the engine to scan the entire string and return all matching expressions instead of stopping immediately at the very first occurrence.
Case-Insensitive (/i)Causes matching boundaries to ignore lowercase vs uppercase letters. For example, /abc/i successfully matches "ABC".
Multiline (/m)Alters anchor behaviors so that ^ and $ match boundaries at the beginning and end of every line, rather than just the entire string bounds.

How to Use the Regular Expression Tester

  1. 1

    Write Your Regex Pattern

    Input your regular expression pattern into the custom slash input box (e.g. ([a-zA-Z]+)). Do not write the enclosing slashes yourself.

  2. 2

    Choose Regex Flags

    Check or uncheck standard flags like global match (g), case-insensitive matching (i), or multiline boundary anchors (m).

  3. 3

    Paste Your Test Text

    Type or paste your source text in the test box. Your matches will be highlighted in real-time, and capture group values will appear in the inspect panel.

Why Use Our Regex Tester Tool?

Regular expressions are incredibly powerful, but their compact syntax can make them exceptionally difficult to read and debug. A single missing modifier or misplaced quantifier can cause the regex to fail completely or capture the wrong text. Our Regex Tester provides instant visual validation. As you compose your regular expression, it highlights matching spans of text and lists capture groups in real-time, allowing you to iterate on your patterns quickly and with confidence.

Regex Reference Cheatsheet

  • \d: Matches any digit character (equivalent to [0-9]).
  • \w: Matches any alphanumeric word character (equivalent to [a-zA-Z0-9_]).
  • \s: Matches any whitespace character (space, tab, newline).
  • +: Matches one or more of the preceding tokens.
  • *: Matches zero or more of the preceding tokens.
  • ?: Makes the preceding token optional (or non-greedy when appended to quantifiers).

Frequently Asked Questions

What is a Regular Expression (Regex)?

A Regular Expression (commonly abbreviated as Regex or Regexp) is a sequence of characters that forms a search pattern. It is used by programmers to perform highly complex search-and-replace actions, validate text inputs (like emails or phone numbers), or parse unstructured logs.

How do capture groups work in Regex?

Capture groups are defined by enclosing a sub-pattern in parentheses, such as '(\w+)'. When the regex engine matches the pattern, it isolates the text captured by these parentheses and reports them as distinct sub-matches. This lets you extract specific substrings from larger matches with ease.

Is it safe to test proprietary data on this tool?

Absolutely. SnapTool operates entirely in your local browser using client-side JavaScript. Your expressions, patterns, and source text never contact any remote tracking servers, offering completely private and safe regex testing.

What do the flags g, i, and m stand for?

Flags change how the regular expression behaves: 'g' (global) finds all matches in the text rather than stopping after the first match. 'i' (case-insensitive) ignores capitalization boundaries (e.g. matching both A and a). 'm' (multiline) causes the start (^) and end ($) anchors to apply to each line instead of the entire string.

Why does my regex result in an infinite loop?

An infinite loop in regex execution typically occurs when using zero-width patterns (like '^' or positive lookaheads) in combination with a global 'g' flag, where the engine makes a match but fails to advance the index. Our tester includes safety index counters to detect and prevent infinite loops instantly.

Share Feedback or Report an Issue

Help us improve this tool. Report bugs, suggest features, or request data updates!