Regex Diff
Compare two regex patterns side-by-side, highlighting token-level differences.
What is Regex Diff?
A diff tool specialized for regex patterns. Unlike a generic text diff, this one tokenizes each regex and aligns them structurally, so a changed quantifier on the same group shows as a single modification rather than a garbled text diff.
How it works
We tokenize both regexes, compute the longest common subsequence of tokens, then render a side-by-side view with additions, deletions, and unchanged tokens color-coded.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Comparing two patterns
Paste two regexes and see where they differ textually — then test sample strings to understand behavioral differences.
Common mistakes
Text diff isn't equivalence
Different text can match identically, and similar text can match differently — semantic equivalence is only approximated.
Frequently asked questions
How does the diff work?
A line- and token-level diff of the two patterns, plus a sample-input comparison to expose behavioral differences.
Can I test my own samples?
Yes — run any string against both patterns and see which one matches.