Regex Tester

What is Regex Tester?

Regex Tester helps developers build and debug regular expressions with live matches and flag controls. It reduces trial-and-error time for validation rules, parsers, and search/replace workflows.

Pattern testing runs fully in your browser; sample data is not transmitted.

How to use Regex Tester

1. 1Enter your regex pattern in the pattern field.
2. 2Add test text where matches should be found.
3. 3Toggle flags like global (g), ignore-case (i), and multiline (m).
4. 4Review highlighted matches and captured groups, then refine the pattern.

Examples

Pattern: /^[\w.-]+@[\w.-]+\.[A-Za-z]{2,}$/

Pattern: /\bPROJ-\d+\b/g on text: 'Fix PROJ-12 and PROJ-98'

Tips & common mistakes

• Anchor patterns (`^`, `$`) when validating entire input strings.
• Escape special characters like `.` and `?` when matching literals.
• Test edge cases: empty values, unicode text, and unexpected separators.

Who uses this tool?

• •Building form validation patterns in frontend apps.
• •Extracting IDs, tags, and tokens from logs.
• •Testing search/replace expressions before editor-wide changes.

Frequently asked questions

Why does my regex match more text than expected?

Greedy quantifiers like `.*` can overmatch. Use non-greedy variants (`.*?`) or tighter character classes.

What does the global `g` flag change?

Without `g`, many engines return only the first match. With `g`, all non-overlapping matches are found.

How do I match across multiple lines?

Use multiline-related flags and explicit classes, depending on whether you need line anchors or dot to span newlines.

Can I test lookaheads and lookbehinds here?

Yes, if your browser regex engine supports them. Some advanced features vary by runtime version.

Why does regex work in one language but not another?

Regex flavor differences (JavaScript, PCRE, Java, etc.) can affect syntax and feature support.