4629 · Developer Tools · v1.0.0
Regex Lab
Explore patterns in an isolated workspace.
Test JavaScript regular expressions, inspect matches and captures, preview replacement and inspect syntax structure in a disposable worker.
Text-only workspace. Never executes input. General limit: 200,000 UTF-16 units per editor; some operations have tighter limits.
Private session · history disabled
Opt in to store up to five recent text transformations on this device. Never stored on an account or synchronized. Files are never included. Disable history stops new saves; Clear history deletes saved items.
How to use Regex Lab
Paste input, select a command and its options, then run the transformation. Review diagnostics before copying or downloading the result. Input is not executed.
Uses the browser’s JavaScript RegExp engine, not PCRE. Patterns run in a worker that is terminated after the computation limit, so pathological backtracking cannot lock the editor. At most 1,000 matches are displayed; truncated scans are labeled. Replacement syntax follows JavaScript ($&, $1 and named captures). Structure is parsed, not explained by AI.
Privacy and boundaries
Editor contents stay in your browser. Transformations run in a disposable worker and are never sent to a formatting or AI service. History starts disabled; enabling it writes text to local browser storage only. Clearing that history removes this tool’s saved entries, not data saved by other applications. The surrounding website may load its normal navigation and analytics, but the utility workspace is excluded from content-interaction capture.
Use the labeled operation selector for the available capabilities. Keyboard users can reach every control with Tab; Ctrl or Command plus K opens the command palette. Copy requires clipboard permission. Download creates a local text file. Clear removes the current workspace; it does not automatically delete an opted-in history. Inputs and outputs are always rendered as text, never as a runnable preview.
What causes regular-expression denial of service?
Some patterns explore exponentially many backtracking paths on particular inputs. Input limits and terminating isolated workers bound the impact here; they do not prove a pattern safe in another application.