Regex Tester
What is Regex Tester
A regular expression (regex) is a sequence of characters that defines a search pattern for matching text. This online regex tester lets you write a pattern, choose flags (global, case-insensitive, multiline, dotAll), and instantly see which parts of your test string match — with yellow highlights in the preview and a list of every match showing its character position and any captured groups.
How to use
- Type your regular expression in the pattern field between the / delimiters.
- Toggle the flags you need: g (find all matches), i (case-insensitive), m (multiline ^ and $), s (dot matches newlines).
- Type or paste the text you want to search in the Test String area.
- See matches highlighted in the preview and listed below with index positions and captured group values.
- Click Clear to reset both fields and start over.
When to use it
Building a route validator for URLs like /users/123 or /products/abc-456? Type \/(\w+)\/(\w[\w-]*) in the pattern field, turn on the g flag, and paste a list of API paths in the test box. You instantly see which paths match and what the two captured segments (resource type and ID) are, all without writing a single line of code.
Frequently asked questions
What flags are available?
Four flags are supported: g (global — find all matches, not just the first), i (case-insensitive matching), m (multiline — ^ and $ match start/end of each line), and s (dotAll — the dot . matches newline characters too).
How do I test capture groups?
Put parentheses around the part you want to capture: (\d+) captures one or more digits. Each match in the list shows the captured group values labelled Group 1, Group 2, etc. Named groups like (?<year>\d{4}) are also supported.
Why does my pattern cause an error?
Common causes: unescaped special characters (use \. instead of . to match a literal dot), unclosed parentheses or brackets, or invalid flag combinations. The error message below the pattern field describes the issue.
Is the g flag required to find all matches?
Yes. Without g, the regex stops after the first match. Enable g to find every occurrence in the test string.
Are my patterns and text sent to a server?
No. All processing runs entirely in your browser using the built-in JavaScript RegExp engine. Nothing leaves your device.
Can I share this tool with my inputs pre-filled?
Yes. The URL updates automatically as you type. Copy it from the address bar or use the Share button — anyone who opens the link will see your exact inputs ready to go.
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