Regex tester

• g — global. Find every match, not just the first.
• i — case-insensitive.
• m — multiline. ^ and $ match line boundaries instead of only string boundaries.
• s — dotall. . matches newlines.
• u — unicode mode. Required for \u{...} and \p{...}.
• y — sticky. Match must start at lastIndex.

• Numbered groups — wrap with parentheses: (\w+). Reference in replacement as $1.
• Named groups — (?<name>\w+). Reference as $<name>.
• Non-capturing — (?:foo|bar). Groups for alternation without producing a capture.
• Back-references — \1 in the pattern matches whatever the first group captured.

• Catastrophic backtracking — nested quantifiers like (a+)+ can hang the engine on long inputs. Prefer non-greedy or atomic alternatives.
• Greedy by default — .* matches as much as possible. Use .*? for the lazy version.
• Anchors — without ^ / $, a regex matches anywhere. Add them when validating full-string formats.
• Escape special chars — . * + ? ( ) [ ] { } | \ ^ $ all need \ when matched literally.

When to reach for it. Use it to build and debug a pattern interactively, watching matches and groups light up against sample text.

When something else is better. JavaScript’s regex engine differs from PCRE, .NET and others — a pattern proven here may behave differently in another language.

The pitfall to watch. Greedy quantifiers and missing anchors are the usual culprits when a regex matches “too much”; test against adversarial input, not just the happy case.

Everything runs on your device. The values you enter are processed locally in this browser tab — EpitomeTool does not send your input to a server, store it, or log it. That means you can use the tool offline once the page has loaded, and refreshing the tab wipes the slate.