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1.0.14 • Public • Published

▒ μFuzzy

A tiny, efficient fuzzy search that doesn't suck. This is my fuzzy 🐈. There are many like it, but this one is mine.¹


uFuzzy is a fuzzy search library designed to match a relatively short search phrase (needle) against a large list of short-to-medium phrases (haystack). It might be best described as a more forgiving String.includes(). Common applications include list filtering, auto-complete/suggest, and searches for titles, names, descriptions, filenames, and functions.

In uFuzzy's default MultiInsert mode, each match must contain all alpha-numeric characters from the needle in the same sequence; in SingleError mode, single typos are tolerated in each term (Damerau–Levenshtein distance = 1). Its .search() API can efficiently match out-of-order terms, supports multiple substring exclusions (e.g. fruit -green -melon), and exact terms with non-alphanum chars (e.g. "C++", "$100", "#hashtag"). When held just right, it can efficiently match against multiple object properties, too.


  • Junk-free, high quality results with any dataset. No need to fine-tune indexing options or boosting params to attain some arbitrary relevance score cut-off.
  • Precise fuzziness control that follows straightforward rules, without returning unexpected matches.
  • Sorting you can reason about and customize using a simple Array.sort() which gets access to each match's stats/counters. There's no composite, black box "score" to understand.
  • Concise set of options that don't interact in mysterious ways to drastically alter combined behavior.
  • Fast with low resource usage - there's no index to build, so startup is below 1ms with near-zero memory overhead. Searching a three-term phrase in a 162,000 phrase dataset takes 5ms with out-of-order terms.
  • Micro, with zero dependencies - currently ~7.5KB min

uFuzzy demo

Charsets, Alphabets, Diacritics

uFuzzy is optimized for the Latin/Roman alphabet and relies internally on non-unicode regular expressions.

Support for more languages works by augmenting the built-in Latin regexps with additional chars or by using the slower, universal {unicode: true} variant. A more simple, but less flexible {alpha: "..."} alternative replaces the A-Z and a-z parts of the built-in Latin regexps with chars of your choice (the letter case will be matched automatically during replacement).

The uFuzzy.latinize() util function may be used to strip common accents/diacritics from the haystack and needle prior to searching.

// Latin (default)
let opts = { alpha: "a-z" };
// OR
let opts = {
  // case-sensitive regexps
  interSplit: "[^A-Za-z\\d']+",
  intraSplit: "[a-z][A-Z]",
  intraBound: "[A-Za-z]\\d|\\d[A-Za-z]|[a-z][A-Z]",
  // case-insensitive regexps
  intraChars: "[a-z\\d']",
  intraContr: "'[a-z]{1,2}\\b",

// Latin + Norwegian
let opts = { alpha: "a-zæøå" };
// OR
let opts = {
  interSplit: "[^A-Za-zæøåÆØÅ\\d']+",
  intraSplit: "[a-zæøå][A-ZÆØÅ]",
  intraBound: "[A-Za-zæøåÆØÅ]\\d|\\d[A-Za-zæøåÆØÅ]|[a-zæøå][A-ZÆØÅ]",
  intraChars: "[a-zæøå\\d']",
  intraContr: "'[a-zæøå]{1,2}\\b",

// Latin + Russian
let opts = { alpha: "a-zа-яё" };
// OR
let opts = {
  interSplit: "[^A-Za-zА-ЯЁа-яё\\d']+",
  intraSplit: "[a-z][A-Z]|[а-яё][А-ЯЁ]",
  intraBound: "[A-Za-zА-ЯЁа-яё]\\d|\\d[A-Za-zА-ЯЁа-яё]|[a-z][A-Z]|[а-яё][А-ЯЁ]",
  intraChars: "[a-zа-яё\\d']",
  intraContr: "'[a-z]{1,2}\\b",

// Unicode / universal (50%-75% slower)
let opts = {
  unicode: true,
  interSplit: "[^\\p{L}\\d']+",
  intraSplit: "\\p{Ll}\\p{Lu}",
  intraBound: "\\p{L}\\d|\\d\\p{L}|\\p{Ll}\\p{Lu}",
  intraChars: "[\\p{L}\\d']",
  intraContr: "'\\p{L}{1,2}\\b",

All searches are currently case-insensitive; it is not possible to do a case-sensitive search.


NOTE: The testdata.json file is a diverse 162,000 string/phrase dataset 4MB in size, so first load may be slow due to network transfer. Try refreshing once it's been cached by your browser.

First, uFuzzy in isolation to demonstrate its performance.


Now the same comparison page, booted with fuzzysort, QuickScore, and Fuse.js:


Here is the full library list but with a reduced dataset (just hearthstone_750, urls_and_titles_600) to avoid crashing your browser:




Else: https://github.com/leeoniya/uFuzzy/issues



npm i @leeoniya/ufuzzy
const uFuzzy = require('@leeoniya/ufuzzy');


<script src="./dist/uFuzzy.iife.min.js"></script>


let haystack = [
    'Super Awesome Thing (now with stuff!)',

let needle = 'feed cat';

let opts = {};

let uf = new uFuzzy(opts);

// pre-filter
let idxs = uf.filter(haystack, needle);

// idxs can be null when the needle is non-searchable (has no alpha-numeric chars)
if (idxs != null && idxs.length > 0) {
  // sort/rank only when <= 1,000 items
  let infoThresh = 1e3;

  if (idxs.length <= infoThresh) {
    let info = uf.info(idxs, haystack, needle);

    // order is a double-indirection array (a re-order of the passed-in idxs)
    // this allows corresponding info to be grabbed directly by idx, if needed
    let order = uf.sort(info, haystack, needle);

    // render post-filtered & ordered matches
    for (let i = 0; i < order.length; i++) {
      // using info.idx here instead of idxs because uf.info() may have
      // further reduced the initial idxs based on prefix/suffix rules
  else {
    // render pre-filtered but unordered matches
    for (let i = 0; i < idxs.length; i++) {

Integrated Search

uFuzzy provides a uf.search(haystack, needle, outOfOrder = 0, infoThresh = 1e3) => [idxs, info, order] wrapper which combines the filter, info, sort steps above. This method also implements efficient logic for matching search terms out of order and support for multiple substring exclusions, e.g. fruit -green -melon.

Match Highlighting

Get your ordered matches first:

let haystack = [

let needle = 'ba';

let u = new uFuzzy();

let idxs = u.filter(haystack, needle);
let info = u.info(idxs, haystack, needle);
let order = u.sort(info, haystack, needle);

Basic innerHTML highlighter (<mark>-wrapped ranges):

let innerHTML = '';

for (let i = 0; i < order.length; i++) {
  let infoIdx = order[i];

  innerHTML += uFuzzy.highlight(
  ) + '<br>';


innerHTML highlighter with custom marking function (<b>-wrapped ranges):

let innerHTML = '';

const mark = (part, matched) => matched ? '<b>' + part + '</b>' : part;

for (let i = 0; i < order.length; i++) {
  let infoIdx = order[i];

  innerHTML += uFuzzy.highlight(

  ) + '<br>';


DOM/JSX element highlighter with custom marking and append functions:

let domElems = [];

const mark = (part, matched) => {
  let el = matched ? document.createElement('mark') : document.createElement('span');
  el.textContent = part;
  return el;

const append = (accum, part) => { accum.push(part); };

for (let i = 0; i < order.length; i++) {
  let infoIdx = order[i];

  let matchEl = document.createElement('div');

  let parts = uFuzzy.highlight(





How It Works

uFuzzy has two operational modes which differ in matching strategy:

  • intraMode: 0 (default) requires all alpha-numeric characters in each search term to exist in the same sequence in all matches. For example, when searching for "cat", this mode is capable of matching the strings below. What is actually matched will depend on additonal fuzziness settings.
    • cat
    • coat
    • scratch
    • cantina
    • tractors are late
  • intraMode: 1 allows for a single error in each term of the search phrase, where an error is one of: substitution (replacement), transposition (swap), insertion (addition), or deletion (omission). The search strings with errors below can return matches containing "example". What is actually matched will depend on additonal fuzziness settings. In contrast to the previous mode, searching for "example" will never match "extra maple".
    • example - exact
    • examplle - single insertion (addition)
    • exemple - single substitution (replacement)
    • exmaple - single transposition (swap)
    • exmple - single deletion (omission)
    • xamp - partial
    • xmap - partial with transposition

There are 3 phases to a search:

  1. Filter filters the full haystack with a fast RegExp compiled from your needle without doing any extra ops. It returns an array of matched indices in original order.
  2. Info collects more detailed stats about the filtered matches, such as start offsets, fuzz level, prefix/suffix counters, etc. It also gathers substring match positions for range highlighting. Finally, it filters out any matches that don't conform to the desired prefix/suffix rules. To do all this it re-compiles the needle into two more-expensive RegExps that can partition each match. Therefore, it should be run on a reduced subset of the haystack, usually returned by the Filter phase. The uFuzzy demo is gated at <= 1,000 filtered items, before moving ahead with this phase.
  3. Sort does an Array.sort() to determine final result order, utilizing the info object returned from the previous phase. A custom sort function can be provided via a uFuzzy option: {sort: (info, haystack, needle) => idxsOrder}.


A liberally-commented 200 LoC uFuzzy.d.ts file.


Options with an inter prefix apply to allowances in between search terms, while those with an intra prefix apply to allowances within each search term.

Option Description Default Examples
intraMode How term matching should be performed 0 0 MultiInsert
1 SingleError

See How It Works
intraIns Max number of extra chars allowed
between each char within a term
Matches the value of intraMode (either 0 or 1) Searching "cat"...
0 can match: cat, scat, catch, vacate
1 also matches: cart, chapter, outcast
interIns Max number of extra chars allowed between terms Infinity Searching "where is"...
Infinity can match: where is, where have blah wisdom
5 cannot match: where have blah wisdom
For intraMode: 1 only,
Error types to tolerate within terms
Matches the value of intraMode (either 0 or 1) 0 No
1 Yes
intraChars Partial regexp for allowed insert
chars between each char within a term
[a-z\d'] [a-z\d] matches only alpha-numeric (case-insensitive)
[\w-] would match alpha-numeric, undercore, and hyphen
intraFilt Callback for excluding results based on term & match (term, match, index) => true Do your own thing, maybe... - Length diff threshold
- Levenshtein distance
- Term offset or content
interChars Partial regexp for allowed chars between terms . . matches all chars
[^a-z\d] would only match whitespace and punctuation
interLft Determines allowable term left boundary 0 Searching "mania"...
0 any - anywhere: romanian
1 loose - whitespace, punctuation, alpha-num, case-change transitions: TrackMania, maniac
2 strict - whitespace, punctuation: maniacally
interRgt Determines allowable term right boundary 0 Searching "mania"...
0 any - anywhere: romanian
1 loose - whitespace, punctuation, alpha-num, case-change transitions: ManiaStar
2 strict - whitespace, punctuation: mania_foo
sort Custom result sorting function (info, haystack, needle) => idxsOrder Default: Search sort, prioritizes full term matches and char density
Demo: Typeahead sort, prioritizes start offset and match length

A biased appraisal of similar work

This assessment is extremely narrow and, of course, biased towards my use cases, text corpus, and my complete expertise in operating my own library. It is highly probable that I'm not taking full advantage of some feature in other libraries that may significantly improve outcomes along some axis; I welcome improvement PRs from anyone with deeper library knowledge than afforded by my hasty 10min skim over any "Basic usage" example and README doc.

Search quality

Can-of-worms #1.

Before we discuss performance let's talk about search quality, because speed is irrelevant when your results are a strange medly of "Oh yeah!" and "WTF?".

Search quality is very subjective. What constitutes a good top match in a "typeahead / auto-suggest" case can be a poor match in a "search / find-all" scenario. Some solutions optimize for the latter, some for the former. It's common to find knobs that skew the results in either direction, but these are often by-feel and imperfect, being little more than a proxy to producing a single, composite match "score".

Let's take a look at some matches produced by the most popular fuzzy search library, Fuse.js and some others for which match highlighting is implemented in the demo.

Searching for the partial term "twili", we see these results appearing above numerous obvious "twilight" results:


  • twirling
  • The total number of received alerts that were invalid.
  • Tom Clancy's Ghost Recon Wildlands - ASIA Pre-order Standard Uplay Activation
  • theHunter™: Call of the Wild - Bearclaw Lite CB-60

Not only are these poor matches in isolation, but they actually rank higher than literal substrings.

Finishing the search term to "twilight", still scores bizzare results higher:


  • Magic: The Gathering - Duels of the Planeswalkers Wings of Light Unlock
  • The Wild Eight

Some engines do better with partial prefix matches, at the expense of higher startup/indexing cost:


Here, match-sorter returns 1,384 results, but only the first 40 are relevant. How do we know where the cut-off is?


Can-of-worms #2.

All benchmarks suck, but this one might suck more than others.

  • I've tried to follow any "best performance" advice when I could find it in each library's docs, but it's a certainty that some stones were left unturned when implementing ~20 different search engines.
  • Despite my best efforts, result quality is still extremely variable between libraries, and even between search terms. In some cases, results are very poor but the library is very fast; in other cases, the results are better, but the library is quite slow. What use is extreme speed when the search quality is sub-par? This is a subjective, nuanced topic that will surely affect how you interpret these numbers. I consider uFuzzy's search quality second-to-none, so my view of most faster libraries is typically one of quality trade-offs I'm happy not to have made. I encourage you to evaluate the results for all benched search phrases manually to decide this for yourself.
  • Many fulltext & document-search libraries compared here are designed to work best with exact terms rather than partial matches (which this benchmark is skewed towards).

Still, something is better than a hand-wavy YMMV/do-it-yourself dismissal and certainly better than nothing.



Date 2023-10
Hardware CPU: Ryzen 7 PRO 5850U (1.9GHz, 7nm, 15W TDP)
SSD: Samsung SSD 980 PRO 1TB (NVMe)
OS EndeavourOS (Arch Linux)
v6.5.4-arch2-1 x86_64
Chrome v117.0.5938.132
  • Each benchmark can be run by changing the libs parameter to the desired library name: https://leeoniya.github.io/uFuzzy/demos/compare.html?bench&libs=uFuzzy
  • Results output is suppressed in bench mode to avoid benchmarking the DOM.
  • Measurements are taken in the Performance secrion of Chrome's DevTools by recording several reloads of the bench page, with forced garbage collection in between. The middle/typical run is used to collect numbers.
  • The search corpus is 162,000 words and phrases, loaded from a 4MB testdata.json.
  • The benchmark types and then deletes, character-by-character (every 20ms) the following search terms, triggering a search for each keypress: test, chest, super ma, mania, puzz, prom rem stor, twil.

To evaluate the results for each library, or to compare several, simply visit the same page with more libs and without bench: https://leeoniya.github.io/uFuzzy/demos/compare.html?libs=uFuzzy,fuzzysort,QuickScore,Fuse&search=super%20ma.

profile example

There are several metrics evaluated:

  • Init time - how long it takes to load the library and build any required index to perform searching.
  • Bench runtime - how long it takes to execute all searches.
  • Memory required - peak JS heap size used during the bench as well as how much is still retained after a forced garbage collection at the end.
  • GC cost - how much time is needed to collect garbage at the end (main thread jank)
Lib Stars Size (min) Init Search
(x 86)
Heap (peak) Retained GC
uFuzzy (try) ★ 2.3k 7.6KB 0.5ms 434ms 28.4MB 7.4MB 18ms
uFuzzy (try)
(external prefix caching)
210ms 27.8MB 7.4MB 18ms
uFuzzy (try)
(outOfOrder, fuzzier)
545ms 29.5MB 7.4MB 18ms
uFuzzy (try)
(outOfOrder, fuzzier, SingleError)
508ms 30.0MB 7.4MB 18ms
Fuse.js (try) ★ 16.6k 24.2KB 31ms 33875ms 245MB 13.9MB 25ms
FlexSearch (Light) (try) ★ 10.7k 6.2KB 3210ms 83ms 670MB 316MB 553ms
Lunr.js (try) ★ 8.7k 29.4KB 1704ms 996ms 380MB 123MB 166ms
Orama (formerly Lyra) (try) ★ 6.4k 41.5KB 2650ms 225ms 313MB 192MB 180ms
MiniSearch (try) ★ 3.4k 29.1KB 504ms 1453ms 438MB 67MB 105ms
match-sorter (try) ★ 3.4k 7.3KB 0.1ms 6245ms 71MB 7.3MB 12ms
fuzzysort (try) ★ 3.4k 6.2KB 50ms 1321ms 175MB 84MB 63ms
Wade (try) ★ 3k 4KB 781ms 194ms 438MB 42MB 130ms
fuzzysearch (try) ★ 2.7k 0.2KB 0.1ms 529ms 26.2MB 7.3MB 18ms
js-search (try) ★ 2.1k 17.1KB 5620ms 1190ms 1740MB 734MB 2600ms
Elasticlunr.js (try) ★ 2k 18.1KB 933ms 1330ms 196MB 70MB 135ms
Fuzzyset (try) ★ 1.4k 2.8KB 2962ms 606ms 654MB 238MB 239ms
search-index (try) ★ 1.4k 168KB RangeError: Maximum call stack size exceeded
sifter.js (try) ★ 1.1k 7.5KB 3ms 1070ms 46.2MB 10.6MB 18ms
fzf-for-js (try) ★ 831 15.4KB 50ms 6290ms 153MB 25MB 18ms
fuzzy (try) ★ 819 1.4KB 0.1ms 5427ms 72MB 7.3MB 14ms
fast-fuzzy (try) ★ 346 18.2KB 790ms 19266ms 550MB 165MB 140ms
ItemsJS (try) ★ 305 109KB 2400ms 11304ms 320MB 88MB 163ms
LiquidMetal (try) ★ 292 4.2KB (crash)
FuzzySearch (try) ★ 209 3.5KB 2ms 3948ms 84MB 10.5MB 18ms
FuzzySearch2 (try) ★ 186 19.4KB 93ms 4189ms 117MB 40.3MB 40ms
QuickScore (try) ★ 153 9.5KB 10ms 6915ms 133MB 12.1MB 18ms
ndx (try) ★ 142 2.9KB 300ms 581ms 308MB 137MB 262ms
fzy (try) ★ 133 1.5KB 0.1ms 3932ms 34MB 7.3MB 10ms
fuzzy-tools (try) ★ 13 3KB 0.1ms 5138ms 164MB 7.5MB 18ms
fuzzyMatch (try) ★ 0 1KB 0.1ms 2415ms 83.5MB 7.3MB 13ms

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