Pinnacle Toolbox

Regex Tester

Test regular expressions with live match highlighting.

Flags: //g

Highlighted Matches

Matches (0)
No matches found
About this Regex Tester
Regex Tester evaluates regular expressions with live match highlighting so you can iterate patterns before shipping them into code. Developers validate emails and IDs; data folks probe log lines; students practice quantifiers and groups. Enter a pattern and sample text, review matches and capture groups, and refine until edge cases pass. Testing is client-side so production log excerpts with personal data need not upload. Regex engines differ slightly across languages—confirm final patterns in the runtime you deploy (JavaScript, Python, Java) and watch for ReDoS-prone catastrophic backtracking on untrusted input. Commit failing and passing sample strings beside the final pattern in code comments. Prefer possessive or atomic constructs carefully when performance is critical. Fuzzy business rules often outgrow regex—migrate to parsers when patterns keep breaking.
How to use
  1. 1Enter the regular expression pattern.
  2. 2Paste representative sample text to test against.
  3. 3Review highlighted matches and capture groups.
  4. 4Adjust flags or the pattern for missed edge cases.
  5. 5Copy the final pattern into your codebase’s regex flavor.
About the Free Regex Tester
Our free regex tester lets you test regular expressions with live match highlighting. Everything runs locally in your browser — no account, no upload to servers, and no waiting.
Whether you searched for "regex tester" or need a reliable developer utility, Pinnacle Toolbox delivers instant results. Join thousands of users who prefer privacy-first tools that work on any device.
Part of our free developer tools online collection, this tool is designed for speed and simplicity. Open it, paste or upload your input, and get results immediately.
Regex Tester Features
  • 100% free with no hidden limits
  • Runs entirely in your browser — data stays private
  • No login, sign-up, or email required
  • Works on desktop, tablet, and mobile
  • Instant processing with no server round-trip
When to Use Regex Tester
  • Debugging and formatting JSON API responses
  • Encoding credentials or tokens for testing
  • Generating secure passwords and UUIDs for development
  • Minifying HTML and CSS before deployment
Frequently asked questions
Do flags like case-insensitive work?
Use the flags your tester exposes (for example, i, g, m) and mirror them in application code.
Why does a pattern work here but fail in Python?
Dialects differ (lookbehinds, escaping). Re-test in the target language.
What are capture groups?
Parentheses remember substrings you can reference in replacements or code.
Can regex parse full HTML or JSON?
Prefer dedicated parsers. Regex is brittle on nested or irregular markup.
What is catastrophic backtracking?
Some patterns explode in time on crafted input—avoid ambiguous nested quantifiers on untrusted text.
JSON Formatter
Format, minify, and validate JSON data.
URL Encoder
Encode and decode URLs and URI components.
JWT Decoder
Decode JWT tokens and inspect header and payload.
Hash Generator
Generate SHA-1, SHA-256, SHA-384, SHA-512, and MD5 hashes.