Regex Visualizer

Visualize regular expressions as syntax diagrams — see the structure of your pattern

Regex Visualizer — Generate Interactive Railroad Syntax Diagrams from Regular Expressions for Learning, Documentation, and Debugging

1. Enter your regular expression in the input field, optionally appending flags after the pattern delimiter (g for global matching, i for case-insensitive, m for multiline mode, s for dot-matches-all, u for full Unicode support). Railroad diagrams (also called syntax diagrams) are a visual notation for formal grammars — they represent each regex component as a graphical path that the matching engine follows, making the pattern's logical structure immediately visible in a way that raw text syntax cannot convey. A complex alternation like (cat|dog|bird)s? becomes a clearly branching diagram showing each animal option and the optional trailing 's'.
2. Click Visualize to render the railroad diagram on the HTML Canvas. Each regex element becomes a distinct visual component: literals appear as rounded rectangular boxes containing the exact text to match, character classes ([a-z]) show as labeled boxes listing the character range, quantifiers (* + ? {'{'}n,m{'}'}) wrap their target element in looping paths that clearly show repetition ranges, groups ((...)) enclose their contents in bordered containers, alternations ({'|'}) fork into parallel paths that merge back after each alternative, and anchors (^ $ \b) mark the start/end of paths with distinctive terminal symbols. The diagram flows left to right following the regex engine's matching direction.
3. Interact with the rendered diagram: scroll to zoom, drag to pan across large diagrams, or click Fit to Canvas to automatically scale the diagram to fill the viewport. Click Download PNG to export the diagram as a high-resolution raster image — perfect for embedding in documentation, blog posts, Stack Overflow answers, classroom materials, or code review comments where a visual explanation communicates regex logic far faster than text. A helpful note reminds users that the visualizer is optimized for educational and moderately complex patterns — extremely long regexes may produce diagrams that are technically correct but visually overwhelming. All parsing and rendering runs entirely in your browser using JavaScript Canvas API — your regex patterns never leave your device.

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