Regex Tester (Logs oriented)

What this tool does

The Regex Tester applies your regular expression to a block of log text and highlights every match. It reports the match count so you can see how many lines or fragments are captured. This is useful for building filters, alert rules, and extraction patterns without running scripts or CLI tools.

When to use this tool

Use it when debugging log noise, validating alert rules, or extracting fields from semi-structured text. It can also support cleanup tasks where you want to verify a pattern before applying it in a pipeline. If you need to compare two log outputs, you can pair this with Text Diff for a side-by-side view.

How it works

The tool compiles your pattern with the flags you provide, then scans the input text for matches. It highlights matched substrings in the output and counts the total number of hits. All processing happens in your browser, so sensitive log content is not sent anywhere.

Example use case

You want to isolate timeout errors from a large log file. Paste the logs, enter a pattern like timeout|timed out with the case-insensitive flag, and run the test. The matches are highlighted so you can confirm the pattern only captures the intended lines before you deploy the filter in production.

Use cases

• Find error lines in a block of log data.
• Test an extraction pattern before deploying a pipeline.
• Validate an alert regex against sample logs.

Notes & limitations

This tester focuses on the JavaScript regex engine, so syntax may differ from other environments such as PCRE or RE2. Very large log files can slow down the browser. For complex patterns, test incrementally and avoid overly greedy expressions that may hang or highlight too much.

Flags like multiline or dotall can dramatically change results. If a pattern works in another tool but fails here, check the flags and escaping rules. For production log pipelines, re-test patterns in the exact runtime environment to ensure consistent behavior.