Regex Tester

This tool is useful when you need to test regex repeatedly for logs, error extraction, or text-cleanup rules. It is built for quick iteration so you can compare matches, counts, and capture groups without leaving the page.

Patterns and input text are processed only in the browser, so you can experiment without uploading them elsewhere.

When to use it

• When you want to extract specific error lines from logs
• When you need to inspect capture groups before using a pattern in code
• When you want to validate whether a pattern really matches the intended text segments

How to reason about patterns and flags

Regex results depend heavily on both the expression and the flags.

• g: use it when you want more than the first match
• i: use it when case-insensitive matching matters
• m: useful when anchors should work line by line on multi-line input
• Capture groups () help you verify extracted subparts, not just whole matches

Common mistakes

• Forgetting g and assuming the pattern is broken because only one result appears
• Missing escapes for special characters
• Ignoring multi-line context when matching log blocks
• Assuming advanced syntax is always available in every browser runtime

Example input

Error: timeout
OK
Error: forbidden

Example output

{
  "count": 2,
  "matches": [
    { "match": "Error: timeout" },
    { "match": "Error: forbidden" }
  ]
}