Regex Tester
Test and debug your regular expressions in real-time.
Stop the guesswork. Our interactive Regex Tester lets you validate your patterns against test strings instantly. See matches highlighted, explore match groups, and fix errors with ease. The perfect utility for any developer working with text processing.
Regex Tester
Test and validate your regular expressions in real-time.
Results
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About This Tool
The Regex Tester is an essential tool for developers, data scientists, and system administrators who rely on regular expressions (regex) for pattern matching and text manipulation. Regex syntax is notoriously dense and difficult to debug. A small typo can lead to unexpected behavior, making a reliable testing environment crucial. This tool provides a real-time sandbox where you can build and validate your regex patterns. As you type your expression, it's instantly applied to your test string, highlighting all matches. It also lists the full match details, including capture groups, so you can verify that your pattern is working exactly as intended. If your regex is invalid, it provides immediate, clear error feedback, saving you from frustrating debugging cycles in your application code. Whether you're parsing log files, validating user input, or scraping web data, this tester streamlines your workflow and boosts your confidence.
How to Use This Tool
- Enter your regular expression in the "Regular Expression" field, without the starting/ending slashes.
- Select the flags you need, such as `g` (global), `i` (case-insensitive), or `m` (multiline).
- Enter the text you want to test your pattern against in the "Test String" field.
- The "Highlighted Matches" box will instantly update to show what parts of your string are matched.
- The "Match Information" box provides details on each match, including the full text and any capture groups.
- If your regex is invalid, an error will appear telling you what is wrong.
In-Depth Guide
The Basics: Anchors and Character Classes
At its core, regex is about matching characters. `[abc]` matches `a`, `b`, or `c`. `[a-z]` matches any lowercase letter. You can use anchors to pin your match to a specific position. `^` matches the start of the string, and `$` matches the end. So, `^cat$` only matches the exact string "cat" and nothing else.
Quantifiers: Specifying How Many
Quantifiers follow a character or group and specify how many times it should repeat. `*` means zero or more times. `+` means one or more times. `?` means zero or one time. You can be specific with curly braces: `{n}` means exactly n times, `{n,}` means n or more times, and `{n,m}` means between n and m times.
Groups and Capturing
Parentheses `()` create a capturing group. This lets you treat part of your pattern as a single unit and also "captures" the text that matched inside it for later use. For example, in `(\d+)-(\w+)`, you can extract the number and the word separately from a string like "123-abc".
Lookaheads and Lookbehinds
These are advanced "zero-width assertions." They let you match something only if it's followed (or preceded) by something else, without making that "something else" part of the match. A positive lookahead `(?=...)` asserts that what follows must match. For example, `cat(?=s)` matches `cat` in "cats" but not in "cat".