Which flavor does the tester use?

JavaScript's RegExp engine — the same your browser runs. For server-side flavors (PCRE, Python, Go), the results are usually identical for common patterns.

Does it show matched groups?

Yes — every capture group (numbered and named) is extracted for each match. Overlapping matches aren't produced — use a global regex with `g` flag for all matches.

Is there a performance warning?

Yes — the tester detects patterns prone to catastrophic backtracking (nested quantifiers) and warns before running. Prevents freezing the browser on adversarial input.

All JS flags: g, i, m, s, u, y. Hover each flag to see its effect. The tester re-runs as you toggle.

Regex Tester | DevTools Surf

DevTools Surf

Example: Regex Tester

A worked example, rendered from real sample data. Sign in to run the tool on your own input.

Input

/\b[A-Z][a-z]+\b/g
---
Alice and Bob went to the Store to buy Coffee and Tea.

Output

Pattern: /\b[A-Z][a-z]+\b/g
5 matches

Match 1 [0–5): "Alice"
Match 2 [10–13): "Bob"
Match 3 [26–31): "Store"
Match 4 [39–45): "Coffee"
Match 5 [50–53): "Tea"

About Regex Tester

Regex Tester preview - Text / String tool

Test regex patterns with match highlighting and group extraction. Part of the DevTools Surf developer suite. Browse more tools in the Text / String collection.

Use Cases

Build and debug validation patterns for forms or inputs
Extract structured data from log files or CSVs
Verify search-and-replace rules before running them in production
Test lookahead and lookbehind assertions interactively

Tips

Flags like /g, /i, /m are supported
Named groups (?<name>...) are highlighted separately
Match count and group extractions shown in results

Fun Facts

Regular expressions were invented by mathematician Stephen Kleene in the 1950s. The term 'regex' wasn't coined until decades later.
Some regex patterns can take exponential time to evaluate — a phenomenon called 'catastrophic backtracking' that has caused real-world outages at Cloudflare and Stack Overflow.
Perl's regex engine was so influential that most modern regex flavors are called 'Perl-compatible' (PCRE), even in languages that have nothing else to do with Perl.

FAQ

Which flavor does the tester use?: JavaScript's RegExp engine — the same your browser runs. For server-side flavors (PCRE, Python, Go), the results are usually identical for common patterns.
Does it show matched groups?: Yes — every capture group (numbered and named) is extracted for each match. Overlapping matches aren't produced — use a global regex with `g` flag for all matches.
Is there a performance warning?: Yes — the tester detects patterns prone to catastrophic backtracking (nested quantifiers) and warns before running. Prevents freezing the browser on adversarial input.
Can I use flags?: All JS flags: g, i, m, s, u, y. Hover each flag to see its effect. The tester re-runs as you toggle.

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