Regex Tester

How to use

1. Type your pattern in the pattern box - leave out the surrounding slashes.
2. Tick flags: g (all matches), i (ignore case), m (multiline), s (dot matches newline), u (unicode).
3. Paste test text. Matches highlight inline and appear in the results list with positions and captured groups.

Use cases

1. Use case: Validate form input Test an email or phone pattern against real user input before shipping your form validation.

2. Use case: Extract patterns from logs Use a pattern like an IPv4 address to find and highlight matching lines in server logs.

Practical tips

Matches highlight as you type, which makes incremental pattern-building practical: start with the literal text, then generalize. Capture groups show separately — wrap the part you actually want to extract, not the whole pattern. Greedy quantifiers (the default) eat as much as possible; add the lazy modifier when a pattern overshoots. Remember the flags: global changes how many matches are found, and case-insensitivity matters more than people expect. Escape metacharacters like dots when you mean a literal dot. Like every tool on this site, the Regex Tester runs entirely in your browser: the data you enter never leaves your device, nothing is uploaded to a server, and the tool keeps working if your connection drops.

Common mistakes

Regex failures concentrate in four habits:

• Forgetting to escape metacharacters — a literal dot needs a backslash, while an unescaped dot matches any character.
• Leaving greedy quantifiers in place when the pattern overshoots; add the lazy modifier to stop at the first valid match.
• Wrapping the whole pattern in parentheses instead of capturing only the part you actually want to extract.
• Ignoring flags: the global flag changes how many matches are found, and case-insensitivity matters more than people expect.

Frequently asked questions