Regex Explain
Translate a regular expression into plain English. Walks the AST and emits a per-part breakdown — what each char-class, group, quantifier, assertion, and alternation actually means. Recognises ~30 common patterns by shape (emails, URLs, UUIDs, etc.). Chains after regex-tester and regex-visualize for the "what does this thing actually do?" hand-off.
About Regex Explain
Paste a regex — with or without `/.../flags` delimiters — and get a plain-English breakdown of what every part does. The tool parses the regex into its AST and walks each node: character classes, groups, quantifiers, assertions, alternation, backreferences, every flag. Recognises ~30 common patterns by shape and tells you when your regex is "an email matcher" or "a UUID pattern". Helpful for code review, learning, or auditing a regex from someone else.
- Category
- inspect
- Input
- Accepts: text/plain.
- Output
- Outputs: application/json.
- Cost
- Free, runs in your browser
- Memory
- low
Common uses
- Decode an unfamiliar regex pulled from a Stack Overflow answer.
- Verify a regex you wrote does what you think it does — read the English, not the symbols.
- Teach regex by example — paste any pattern, see the structure.
- Audit production regexes for accidental behaviour (greedy quantifiers, missing anchors, unintended backtracking).
- Compose into chains: tester → visualize → explain — three views of the same regex.
Frequently asked questions
Does it accept patterns from other languages (Python, PCRE, .NET)?
The parser targets JavaScript regex syntax. Most patterns work as-is, but a few constructs vary: PCRE-only features like `\K` and atomic groups are unrecognised, .NET-style balanced groups are not supported. For mainstream patterns (anchors, char classes, quantifiers, captures, alternation, lookarounds) the breakdown is correct across flavours.
What does "Recognised pattern" mean?
The tool keeps a curated table of common patterns (emails, URLs, UUIDs, IPv4/6, ISO dates, hex colors, etc.). When your input matches one of these exactly, the summary names it ("Recognised pattern: Email addresses.") so you don't have to puzzle through the breakdown to know what it does.
Does it explain flags?
Yes — the summary lists active flags and what they do: `g` (global), `i` (case-insensitive), `m` (multiline), `s` (dotall), `u` (unicode), `y` (sticky).
Keywords
- regex
- regexp
- explain
- breakdown
- annotate
- pattern
- translate