Named date fields
(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2}) with dgmShows each match plus named year, month, and day captures with their UTF-16 offsets.
🎯Regex TesterReady
Private local testing with a responsiveness guard. Your pattern, test text, replacement, and export remain in this browser. Each run uses an isolated worker that is stopped after 400 ms; that protects this tab, but it is not a proof that a pattern is safe for unbounded server-side input.
0 / 2,000 characters
//
Use Ctrl/Cmd + Enter in the pattern or test text to run. JavaScript positions are UTF-16 code-unit offsets; turn on d to see capture offsets.
122 / 100,000 characters per run
Capability checkedVerified September 9, 2026
What works
- Validate ECMAScript flags before compiling the pattern
- Evaluate a requested match or replacement in a short-lived browser worker rather than the editor's UI thread
- Stop a worker that exceeds the 400 ms responsiveness budget
Important limits
- The worker timeout protects this browser tab, not a production service that runs the same pattern against unbounded or hostile input
- The ReDoS shapes are a deliberately incomplete warning heuristic, not a proof that a pattern is safe or unsafe
What the Regex Tester does—and does not do
Exact supported inputs, outputs, limits, and primary sources for the current implementation.
Accepted input
- A JavaScript regular-expression pattern up to 2,000 characters and any supported ECMAScript flags
- Up to 100,000 characters of local test text, an optional UTF-16 start offset for global or sticky matching, and an optional replacement string
- ECMAScript d, g, i, m, s, u, v, and y flags, except the mutually exclusive u and v pair
Produced output
- Up to 250 match values with numbered and named capture groups
- UTF-16 match and capture ranges when d (indices) is supported and enabled
- A locally evaluated replacement preview and a JSON export of settings and match data without the raw test text
- A transparent warning for representative nested-quantifier, overlapping-alternation, or adjacent-wildcard shapes
Operational limits
- Patterns are limited to 2,000 characters, test text to 100,000 characters, visible matches to 250, and each worker run to 400 ms
- The workbench runs JavaScript regular expressions only; syntax and behavior can differ in PCRE, Python, .NET, Java, RE2, and database engines
- Start offset and displayed ranges are UTF-16 code-unit offsets, not grapheme-cluster positions
Known limitations
- The worker timeout protects this browser tab, not a production service that runs the same pattern against unbounded or hostile input
- The ReDoS shapes are a deliberately incomplete warning heuristic, not a proof that a pattern is safe or unsafe
- d and v availability depends on the visitor's browser; an unsupported feature returns the browser's compile error
- Replacement follows JavaScript semantics and the JSON export intentionally omits the full test text, though matched values remain in the export
Standards and primary sources
Capability claims last reviewed September 9, 2026. Review dates describe the implementation audit, not content freshness by itself.
Use the Regex Tester with the right expectations
A regex tester should show the runtime it uses and make its boundaries visible. This workbench evaluates only when you request it, in a short-lived browser worker with explicit pattern, sample, match-count, and time limits. It supports current JavaScript flags, zero-length Unicode matching, named captures, d-flag offsets, native replacements, and match-data export that deliberately excludes the full sample.
When it is the right tool
- Debugging JavaScript flags, global/sticky behavior, and a specific start offset
- Inspecting numbered and named capture groups with d-flag ranges
- Testing a replacement without freezing the editor on a pathological sample
- Exporting pattern settings and match metadata without exporting the complete test text
A deliberate choice
Tooleras keeps this page specific to the job above instead of claiming support for adjacent formats, platforms, or edge cases it cannot verify. Open the capability guide for the exact inputs, outputs, limits, and sources.
Checked examples
A risk signal, not a verdict
(a+)+$ against a near-miss sample
Warns about nested unbounded repetition and stops the isolated worker after the responsiveness budget if evaluation runs too long.
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