What JavaScript Regex Tester does

The tester runs JavaScript RegExp syntax against submitted text only after an explicit action and shows each match without inserting it as HTML.

How to use it

• Enter a JavaScript pattern and flags.
• Add test text and an optional replacement.
• Choose Run test.
• Review indices, values, groups and replacement preview.

Practical example

The named-group example captures each word and previews bracketed replacements.

Technical methodology

Native RegExp provides JavaScript-engine behavior. The loop advances after zero-length matches, caps visible results at 1,000 and rejects obvious nested-repeat risks.

Common uses

• Debug JavaScript patterns
• Inspect capture groups
• Preview replacements
• Learn flag behavior

Common errors

• Invalid or duplicate flags
• Malformed JavaScript syntax
• Oversized fields
• Obvious expensive-pattern heuristic

Security and privacy

Pattern and text remain local and are rendered as text. Execution is explicit, capped and never uses eval.

Limitations

Risk detection is heuristic and cannot guarantee protection from every catastrophic-backtracking expression. Other regex engines differ.