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safe rewrites · behaviour-preserving · local

Shrink a regex without changing what it matches

Apply nine behaviour-preserving rewrites — \\d for [0-9], + for {1,}, drop redundant non-capturing groups — and copy the shorter result. Runs locally.

Regex Simplifier
Before
33
chars
After
9
chars
Saved
24
bytes
Rules
9/9
active
input · pattern + rule toggles
Rewrites
output · simplified pattern
Result
abc\d+\w?
before: 33 bytesafter: 9 bytessaved: 24 bytes
Quick Start

How to simplify a regex

Apply safe, behaviour-preserving rewrites that shrink your pattern without changing what it matches.

  1. 01

    Paste pattern

    Drop your regex in. Every applicable rewrite previews in the output as you type.

    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.

    patternECMAScriptliterallive
    input · literalregex · regex
    (?:abc)[0-9]{1,}
    loaded · ECMAScriptPCRE · ready
  2. 02

    Toggle rules

    Each rewrite is opt-in. Disable any you'd rather skip.

    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 · mlive
    config · optionsrules · flags
    [x] {1,} -> +
    flags applied · liveECMA · live
  3. 03

    Compare lengths

    Saved bytes show how much shorter the output is. Behaviour stays identical.

    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-safe
    run · outputsaved · matches
    before 27 after 18 saved 9
    matches · livegroups · live
  4. 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.

    copyexportclipboardblob
    export · exportedready · saved
    Copied
    ready to shipsuccess
Pro tips

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&rsquo;t parsers

Don’t parse HTML, JSON, or balanced parens with regex. Use a proper parser when the grammar is recursive.

Related toolsRegex ExplainerRegex TesterRegex BuilderRegex CheatsheetRegex Character ClassesRegex Diff
Use Cases

When to simplify

A shorter regex is easier to read, audit, and ship.

Code-review polish

Shrink a sprawling pattern before merging. 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-safe

Readability

\d reads better than [0-9] in most code. 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-compliant

Bundle size

Long regex literals add up in client JS. 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-grade

Educate

Show why {1,1} is redundant. 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-engine

Refactor legacy

Sweep an old regex set into modern equivalents. 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-ready

Audit equivalence

Every rule is provably behaviour-preserving. 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-ready
FAQ

Frequently asked questions

Yes — each rule preserves the language matched by the regex. Test with your sample text to be sure.
All are on by default. Untick anything you'd rather keep verbatim — e.g. you may prefer [0-9] over \d.
Yes for simple sets like [0-9] and [A-Za-z0-9_]. Complex sets with negation or ranges are left alone.
{1,1}, {1,}, {0,1}, {0,} all rewrite to their canonical short forms.
No. The tool runs entirely in your browser — your pattern and sample text never leave the page.
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