Toolivaro

Free Regex Tester

Test regular expressions live against your own text with match highlighting, capture groups, and flags — fully local.

Processed locally in your browser

Flags

How is the result calculated?

Extracting IDs from log lines

Given log lines like "2026-08-05 09:30 ERROR request_id=7f3a user=ada", the pattern /request_id=(\w+)/g matches each request id and captures the value into group 1. The tester lists both matches with positions and their captured groups, so you can confirm the pattern before using it in a log pipeline.

Input Value
text 2026-08-05 09:30 ERROR request_id=7f3a user=ada 2026-08-05 09:31 ERROR request_id=9c21 user=bob
pattern request_id=(\w+)
flags g
Result 2 matches · group 1: 7f3a, 9c21

What is the formula and its assumptions?

Matching semantics

matches = text.scan(pattern, flags)

Symbol Meaning
pattern ECMAScript regular expression (platform RegExp engine)
flags g (global), i (ignore case), m (multiline), s (dot-all), u (unicode), y (sticky)

Behavior is exactly the platform engine’s — what matches here matches in JavaScript, Node.js, and browsers.

What are the most common mistakes?

  • Testing with the g flag but reading only the first result — with /g the engine advances through every match.
  • Expecting PCRE features (like lookbehind before ES2018) in an ECMAScript pattern.
  • Forgetting that . does not match newlines unless the s flag is set.
  • Pasting patterns or text containing secrets into a web service — this tool is fully local.

What are the assumptions and limitations?

  • The dialect is ECMAScript only; PCRE/RE2-style features not in ECMAScript are rejected with the platform error.
  • Match scanning is capped for safety; extremely large texts or pathological patterns may be truncated with a notice.
  • The tool shows what the engine matches — it cannot judge whether a pattern is efficient or safe for a production workload.

Where do the numbers come from?

Last reviewed August 5, 2026 · Version 1.0.0 · Toolivaro does not guarantee external content.

Frequently asked questions

Which regex dialect does this tool use?

The platform’s ECMAScript engine — the same dialect JavaScript, Node.js, Deno, and browsers use. Dialects like PCRE (PHP, grep, regex101’s default) have extra features such as lookbehind in different forms and named groups with different syntax; those are not part of ECMAScript.

Why did my pattern match nothing?

Common causes: missing the g flag when you expect multiple matches, forgetting that anchors like ^ and $ match line boundaries only with the m flag, and patterns that accidentally include literal spaces. The tool shows every match with its position so the failure is usually visible at a glance.

Is my text sent anywhere?

No. The pattern and the text are processed entirely in your browser tab — nothing is uploaded, logged, or stored. This matters for log excerpts and configuration files that often contain credentials or personal data.

Found a mistake or have a correction? Report it — we review every correction.