Regex Lab — Test • Match • Replace

Instant regex tester: flags, live highlights, groups, and replace preview. Works fully offline. No permissions.

Regex Lab is a lightweight, offline regular-expression tester built for clarity and speed. Enter a pattern, pick flags (i, g, m, s, u, y), paste test text, and see live highlighting, match counts, execution time, capture groups, and an optional Replace preview (supports $1, $2, …). You can copy the highlighted HTML or copy the replaced output in one click. Why it’s safe and easy to approve No permissions required (no tabs, no storage, no clipboard permission). Works fully offline — nothing leaves your browser. No site access and no content scripts; it doesn’t modify web pages. No background tasks, no tracking, no external network requests. MV3 & CSP-friendly: no inline scripts or remote assets. Key features Test patterns with live feedback and error messages for invalid regex. Flags: toggle i g m s u y as needed. Highlight all matches in a clean preview pane. Matches & groups: view each match with start index, length, and captured groups. Replace preview with $1, $2, … placeholders. Copy highlighted HTML or replaced output instantly. Accessible, keyboard-friendly UI with a compact “terminal” theme. Designed for developers, QA, writers, and anyone who needs fast, privacy-first regex testing inside a simple popup.