Regex Tester — About

Dive deeper into how the Regex Tester evaluates patterns, keeps data on-device, and supports RE2 safety mode.

Key points

What this guide covers

Review core capabilities, privacy considerations, and the difference between browser regex engines and RE2 safety mode.

People-first explanations

We explain flags, capturing groups, named groups, and highlight behaviour so stakeholders without deep regex knowledge can collaborate.

Limitations and roadmap

Understand where RE2 compatibility checks stop and learn about planned enhancements like saved pattern libraries.

The Regex Tester is designed for engineers, analysts, and support teams who need fast insight into how a regular expression behaves. It keeps evaluation local to your browser, highlights matches in real time, and records capture groups alongside named groups so you do not have to mentally parse dense output.

Key capabilities

Toggle-friendly interface for the six most common JavaScript regex flags.
Live highlighting that renders zero-length matches with an accessibility-friendly marker.
JSON export of matches so you can paste results into bug reports or documentation.
RE2 compatibility guardrails to spot unsupported constructs before they reach production.

Privacy posture

Patterns and test strings never leave the page unless you copy them. When you use the share link feature we base64url-encode the inputs inside the URL so recipients can recreate the same session. Remove secrets, API keys, and customer data prior to sharing to stay compliant with security policies.

Performance and roadmap

The tool comfortably handles kilobytes of sample text. For extremely large payloads consider a dedicated scripting environment. Upcoming improvements include saved pattern presets, integration with team knowledge bases, and optional RE2-WASM execution for absolute parity with RE2 runtime.

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How to use this tool

Step 1
What the tool does
It executes your regular expression against sample text, highlights matches, and surfaces captures so you can iterate quickly on validation logic.
Step 2
How to use it effectively
Start with simple inputs, toggle flags deliberately, and use the JSON copy button to share exact match data with teammates reviewing your pattern.
Step 3
Limitations to keep in mind
The RE2 checker is heuristic-based and the underlying engine is XRegExp (JavaScript). Test final patterns in your production runtime before deploying critical validation rules.

Frequently asked questions

Does the Regex Tester store my pattern or sample text?: No. Everything runs in your browser and clears when you refresh unless you copy a share link. Those links embed your inputs in the URL so review them before sharing externally.
What is RE2 safety mode really checking?: RE2 mode looks for constructs the RE2 engine rejects (like lookbehinds and backreferences) and flags nested quantifiers that often lead to catastrophic backtracking. It is a conservative heuristic but catches the most common production issues.
When should I disable certain flags?: Match the environment you target. For example, turn off the global flag if you only need the first match or disable Unicode if your runtime does not support it yet. The tester mirrors what your application will do.

Share links expose your pattern and sample text. Avoid including personal or production data when collaborating and prefer anonymised payloads for documentation.