Just Tool It /
Regex Tester
On-device — nothing uploaded
Regex Tester
Test JavaScript regular expressions against sample text. Matches highlight as you type.
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Why test regex on-device?
Regex sandboxes are where people paste production logs, emails, and customer IDs. A cloud tester retains that sample. Just Tool It evaluates expressions with the browser’s RegExp engine against text that never leaves the page — highlight matches, inspect capture groups, iterate safely.
How to use the regex tester
- Enter a pattern and flags (g, i, m, s, u, y as supported).
- Paste sample text you want to match.
- Review highlights, match lists, and capture groups.
- Refine the pattern until edge cases pass — then copy into your code.
Frequently asked questions
Is this JavaScript regex or PCRE?
It follows JavaScript RegExp semantics (the engine in your browser). Patterns can differ from Python,
PCRE, or Go flavors.
Can catastrophic backtracking freeze the tab?
Pathological patterns on large inputs can be slow. Start with small samples; avoid nested unbounded
quantifiers when possible.
Is my sample text uploaded?
No. Matching is local. Safe for redacted production logs.
Does it support replace?
If the UI includes a replace field, substitution runs with JS String.replace semantics; otherwise use
matches to craft your own replace in code.