Read any regex as plain English
Drop in a pattern and get a token-by-token breakdown — anchors, classes, groups, quantifiers — all explained in order.
- 1.
^start of string/line - 2.
(?<user>start named capturing group "user" - 3.
[\w.+-]any character in [\w.+-] - 4.
+1 or more (greedy) of the previous - 5.
)end group - 6.
@the literal character '@' - 7.
(?<host>start named capturing group "host" - 8.
[\w.-]any character in [\w.-] - 9.
+1 or more (greedy) of the previous - 10.
)end group - 11.
\.the literal character '.' - 12.
[A-Za-z]any character in [A-Za-z] - 13.
{2,}repeat the previous 2, times - 14.
$end of string/line
How to read a regex token-by-token
Type any ECMAScript pattern and read what each piece does, in order, in plain English — anchors, character classes, capture groups, lookarounds, and quantifiers all called out by name.
- 01
Paste a pattern
Drop in any regex — short or sprawling, inherited from a teammate, copied from Stack Overflow, or pulled from a config file. The explainer walks it strictly left-to-right and handles ECMAScript syntax including named capture groups, lookahead, lookbehind, and Unicode property escapes.
Patterns compile through the JavaScript RegExp constructor, so syntax errors surface immediately and engine quirks like Unicode property escapes (\p{L}) work when the u flag is on.
patternECMAScriptliteralliveinput · pattern · literalECMAScript · live · regex^[A-Z]\d{3}$loaded · ECMAScriptPCRE · ready - 02
Read each token in English
Every anchor (^, $, \b), character class ([A-Z], \d, \w), capture group ((?<name>...)), lookaround ((?=...), (?!...)), and quantifier (*, +, ?, {n,m}) becomes a numbered line with its plain-English meaning. The breakdown surfaces both the literal token and its semantic role.
Each flag character mirrors the ECMAScript literal: g enables iteration, i folds case, m anchors per line, s lets . match newlines, u unlocks proper Unicode, y is sticky, and d emits indices.
flagsoptionsg · i · mliveoutput · english · optionstokens · ordered · flags1. ^ start of string 2. [A-Z] uppercase letter 3. \d{3} exactly 3 digits 4. $ end of stringflags applied · liveECMA · live - 03
Sanity-check intent
Spot stray dots that should be escaped, accidental greedy quantifiers that swallow more than intended, missing anchors that let the regex match mid-string, or duplicated alternation branches. The numbered walk makes drift between intent and implementation obvious in seconds.
Watch for catastrophic backtracking on nested quantifiers — a common ReDoS source. The tool caps match counts to keep the page responsive on pathological patterns.
matchgroupshighlightReDoS-safeaudit · review · outputfix · refine · matchesno surprises · anchors set · greedy offmatches · livegroups · live - 04
Copy or export
Grab the output as JSON, CSV, or plain text — ready for your editor or pipeline.
Copy writes via navigator.clipboard.writeText; downloads use a Blob and object URL, so nothing transits the network and the output is byte-identical to what you see on screen.
copyexportclipboardblobexport · exportedready · savedCopiedready to shipsuccess
Regex patterns that don't melt down
Use named groups
(?<year>\d{4}) reads better than $1 and survives reordering. Supported in ECMAScript 2018+.
Anchor strictly
Use ^/$ with the m flag when matching whole lines. Without anchors, partial matches sneak through.
Avoid catastrophic backtracking
Nested quantifiers like (a+)+ can explode. Run patterns through ReDoS Detector first.
Escape every literal
Backslash any meta character you want literally: \.\$\^\*\+\?\(\)\[\]\{\}\|\\.
Test edge cases
Empty string, single character, unicode, the maximum length you expect — write fixtures for each.
Patterns aren’t parsers
Don’t parse HTML, JSON, or balanced parens with regex. Use a proper parser when the grammar is recursive.
When explanations help
Turn cryptic patterns into shareable prose.
Onboard new devs
Translate inherited patterns into prose for code reviews. Compiles through the JavaScript RegExp constructor — engine quirks (Unicode property escapes, sticky matching, named groups) work when their flags are on. Error messages cite the exact position of any syntax issue.
ReDoS-safeDebug match failures
See exactly what each token contributes to a misbehaving regex. Pairs with the ReDoS detector to catch catastrophic backtracking before you deploy. A pattern that handles 1k-character input fine can become a denial-of-service vector on attacker-controlled 1M-character input.
ECMA-compliantSpot redundancy
Find duplicated alternatives or unused groups quickly. Output exports as JavaScript, Python re, Java util.regex, .NET System.Text.RegularExpressions, PCRE, and POSIX — language quirks are highlighted on conversion so you don't ship a JS-only pattern to a Go service.
spec-gradePair-explain
Share an explanation by URL or copy-paste in chat. Capture groups (named or numbered) round-trip cleanly into replacement strings, JSON output, or CSV extraction without re-typing. Backreferences ($1, ${name}) preserve semantics across languages.
cross-engineDocument a pattern
Generate inline comments from the breakdown. Test against edge cases — empty input, single character, max length, multibyte boundaries — to catch off-by-one and zero-length match bugs before they reach production.
test-readyLearn by example
Walk through a real pattern instead of dry syntax tables. All matching runs client-side so secret patterns never leave the browser. Useful when the pattern itself is sensitive (PII regexes, internal data formats, security filters).
production-readyFrequently asked questions
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