Regex Builder

About this tool

Build a regular expression by choosing what to match, digits, letters, a length range, and whether to anchor the whole string. See the pattern and test it live.

Example

Input: digits, anchored, min 3

Output: /^[0-9]{3,}\$/

Privacy

This tool runs entirely in your browser. Your data is processed locally and never uploaded to a server.

How to use this tool

1. Choose what the pattern should match, such as digits, letters, an email, or a custom range.
2. Set the length range if you need a fixed count or a minimum and maximum length.
3. Turn on anchors if the whole string must match from start to end.
4. Read the generated regular expression and test it against sample text in the live tester.

Step by step, what happens

1. You start by selecting the kind of content you want the regex to recognize, which narrows the pattern to a common case like digits, letters, or email.
2. The tool then combines your choices into a regular expression, including length limits and optional start and end anchors when needed.
3. As you change options, the pattern updates immediately so you can see exactly what was generated.
4. You can paste test strings into the live area to confirm whether the regex matches the text you expect.

Worked example

Suppose you need a regex that matches exactly 5 digits, such as a simple code.

Input: 12345

1. Select digits as the content type and set the length to exactly 5.
2. Enable anchoring so the whole string must be digits and nothing else.
3. The tool generates a pattern for a 5 digit string and shows it live in the output area.

Tips and common mistakes

• Use anchors when you want the entire input to match, not just part of it.
• Be careful with length settings, since a fixed length and a range can produce very different matches.
• Choose the simplest content type that fits your case, since digits, letters, and email are easier than building a custom pattern by hand.
• Test with both valid and invalid examples so you can see whether the generated regex is too strict or too loose.

Frequently asked questions