UnderscoreJS 1.12.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 68271 bytes (66.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 19466 bytes (19.0k, 29%).

After GZIP compression these minified files vary in size:

unpkg	8266 bytes (8.1k)	CDN
Boot	7498 bytes (7.3k)	CDN
cdnjs	7494 bytes (7.3k)	CDN
gzip -6 (default)	7492 bytes (7.3k)	local copy
gzip -9	7483 bytes (7.3k)	local copy
libdeflate -12	7301 bytes (7.1k)	local copy
kzip -s0 -rn -b2	7289 bytes (7.1k)	local copy
7zip -mx=9 -tgzip	7287 bytes (7.1k)	local copy
zultra	7286 bytes (7.1k)	local copy
pigz -11 -n	7280 bytes (7.1k)	local copy
Zopfli	7269 bytes (7.1k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.12.1.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.12.1 file, ETag caching is available and
if your browser doesn't support GZIP decompression then the uncompressed version will be sent.

Currently best Zopfli settings

Save 225 bytes by using my UnderscoreJS 1.12.1 Zopfli version instead of the best available CDN (3.10% smaller than cdnjs, 7269 vs. 7494 bytes):

Download

You can use my super-compressed files for whatever purpose you like as long as you respect the library's original license agreement.
There are no restrictions from my side - but please avoid hot-linking if you run a high-traffic website.

These command-line settings yielded the best compression ratio so far (Linux version of zopfli-krzymod):
zopfli --i100000 --mb8 --mls2048 --bsr15 --lazy --ohh

(found April 6, 2021)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	2048	--mls2048
block splitting recursion	15	--bsr15
lazy matching in LZ77	yes	--lazy
optimized Huffman headers	yes	--ohh
initial random W for iterations	1	--rw1
initial random Z for iterations	2	--rz2

Verify file integrity

After decompression, my uncompressed files are identical to the original ones:

MD5:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.12.1/underscore-min.js --location | md5sum
f836abbb789375d11ce1092a0f4385c0 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.12.1.min.zopfli.js.gz | md5sum
f836abbb789375d11ce1092a0f4385c0 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.12.1/underscore-min.js --location | sha1sum
6bbbb25f5bcb7c4e5f07a5490107f262f5f261bb -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.12.1.min.zopfli.js.gz | sha1sum
6bbbb25f5bcb7c4e5f07a5490107f262f5f261bb -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	7498 bytes	f836abbb789375d11ce1092a0f4385c0	(invalid)
cdnjs	7494 bytes	f836abbb789375d11ce1092a0f4385c0	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
unpkg	8266 bytes	9ee425aa01bab40af5934eec1fc71cab	< var n="1.12.1",r="object"==typeof self&&self.self===self&& [...] > var n="1.12.1",r="object"==typeof self&&self.self===self&& [...]	(invalid)

Note: only the MD5 hashes are shown to keep things simple.

Other Versions

Available UnderscoreJS versions at minime.stephan-brumme.com:

1.13.6, 1.13.5, 1.13.4, 1.13.3, 1.13.2, 1.13.1, 1.13.0,
1.12.1, 1.12.0,
1.11.0,
1.10.2, 1.10.1, 1.10.0,
1.9.2, 1.9.1, 1.9.0,
1.8.3, 1.8.2, 1.8.1,
1.7.0,
1.6.0,
1.5.2, 1.5.0,
1.4.4, 1.4.3, 1.4.2, 1.4.1, 1.4.0,
1.3.3, 1.3.2, 1.3.1, 1.3.0,
1.2.4, 1.2.3, 1.2.2, 1.2.1, 1.2.0,
1.1.7, 1.1.5, 1.1.4, 1.1.3, 1.1.2, 1.1.1, 1.1.0,
1.0.4, 1.0.3, 1.0.2, 1.0.1, 1.0.0,
0.6.0,
0.5.7, 0.5.6, 0.5.5, 0.5.4, 0.5.3, 0.5.2, 0.5.1, 0.5.0,
0.4.7, 0.4.6, 0.4.5, 0.4.4, 0.4.3, 0.4.2, 0.4.1, 0.4.0,
0.3.3, 0.3.2, 0.3.1, 0.3.0,
0.2.0,
0.1.1, 0.1.0

The project site contains an overview how well these versions were compressed.
Other interesting projects are AngularJS, BackboneJS, Bootstrap, D3, Dojo, Ember, jQuery, Knockout, lodash, React, Socket.IO, ThreeJS and Vue.

Changelog

Best Zopfli parameters so far:

Size	Improvement	Parameters	Found
7269 bytes	-1 byte	zopfli --i100000 --mls2048 --bsr15 --lazy --ohh	April 6, 2021 @ 19:41
7270 bytes	-1 byte	zopfli --i10000 --mls2048 --bsr15 --lazy --ohh	April 6, 2021 @ 18:00
7271 bytes	-1 byte	zopfli --i10000 --mls2048 --bsr9 --lazy --ohh	April 6, 2021 @ 17:58
7272 bytes	-2 bytes	zopfli --i1000 --mls16384 --bsr4 --lazy --ohh	April 6, 2021 @ 17:24
7274 bytes	–	zopfli --i100 --mls32768 --bsr21 --lazy --ohh	April 6, 2021 @ 16:26

If there are multiple parameter sets yielding the same compressed size, only the first one found is shown.

Most recent activity on April 7, 2021 @ 10:17.

Heatmaps

This Zopfli heatmap visualizes how compression changes when modifying the --bsr and --mls parameter.
Cell's contents is the best filesize achieved (in bytes, hover with mouse over cells to see number of iterations).

Good parameters are green, bad are red. The best and worst are bold as well.
The brightness of the blue background color indicates how many iterations were processed:
10,000, 100,000 or 1,000,000.

bsr \ mls	2	4	8	16	32	64	128	256	512	1024	2048	4096	8192	16384	32768
bsr \ mls	2	4	8	16	32	64	128	256	512	1024	2048	4096	8192	16384	32768
2	7272	7272	7272	7279	7279	7279	7279	7272	7273	7275	7273	7275	7273	7271	7271
4	7277	7285	7277	7276	7275	7276	7276	7275	7281	7280	7273	7271	7271	7272	7271
6	7279	7278	7278	7280	7278	7278	7279	7279	7279	7277	7273	7278	7278	7274	7271
7	7278	7278	7278	7275	7275	7272	7273	7273	7281	7274	7274	7271	7272	7272	7272
8	7280	7278	7285	7275	7276	7276	7276	7274	7273	7277	7271	7271	7271	7271	7271
9	7278	7278	7276	7275	7275	7276	7275	7276	7276	7273	7271	7271	7273	7271	7273
10	7284	7271	7287	7288	7276	7271	7274	7274	7276	7277	7273	7272	7278	7272	7273
11	7285	7272	7284	7276	7278	7277	7275	7274	7273	7278	7273	7271	7279	7271	7271
12	7278	7278	7276	7275	7276	7276	7276	7275	7281	7272	7273	7271	7271	7272	7272
13	7276	7278	7278	7275	7276	7276	7278	7279	7279	7273	7273	7272	7273	7271	7271
14	7278	7278	7284	7278	7276	7285	7276	7275	7273	7277	7273	7271	7271	7272	7271
15	7278	7277	7278	7276	7276	7276	7276	7275	7276	7271	7269	7271	7278	7272	7270
16	7277	7278	7278	7277	7278	7275	7277	7277	7277	7278	7273	7271	7271	7272	7271
17	7278	7278	7285	7276	7275	7275	7276	7274	7272	7279	7271	7273	7274	7271	7271
18	7278	7278	7278	7276	7276	7275	7277	7275	7276	7277	7273	7273	7274	7271	7271
19	7278	7278	7278	7276	7276	7275	7276	7274	7272	7278	7271	7274	7278	7271	7271
20	7278	7278	7278	7275	7276	7285	7279	7278	7273	7277	7273	7273	7278	7272	7272
21	7279	7278	7276	7278	7276	7275	7279	7278	7275	7278	7273	7271	7274	7271	7271
22	7278	7277	7276	7275	7276	7275	7279	7278	7272	7273	7273	7278	7278	7271	7271
23	7278	7278	7276	7276	7277	7277	7276	7278	7276	7277	7273	7278	7275	7272	7272
25	7278	7278	7278	7275	7276	7276	7272	7278	7273	7277	7273	7273	7275	7271	7271
30	7278	7278	7276	7276	7277	7275	7275	7276	7276	7278	7273	7271	7271	7272	7272
40	7279	7277	7276	7276	7276	7275	7276	7275	7273	7279	7271	7272	7278	7274	7273

Due to the Monte Carlo design of my search algorithm, not all parameters have reached the same number of iterations yet:

Iterations	Min. Bytes	Reduction	Coverage
100	7274 bytes	–	100%
1,000	7272 bytes	-2 bytes	100%
10,000	7270 bytes	-2 bytes	100%
100,000	7269 bytes	-1 byte	0.58%
1,000,000	7269 bytes	–	0.29%
10,000,000	–	–	–

KZIP has far less options available for tuning/optimization. I only played around with the number of blocks (parameter -n):

Blocks	Min. Bytes	Compared To Best Zopfli	Compared To Best KZIP
(any)	7291 bytes	+22 bytes (+0.30%)	+2 bytes
1	7291 bytes	+22 bytes (+0.30%)	+2 bytes
2	7289 bytes	+20 bytes (+0.28%)	–
3	7310 bytes	+41 bytes (+0.56%)	+21 bytes
4	7337 bytes	+68 bytes (+0.94%)	+48 bytes
5	7365 bytes	+96 bytes (+1.32%)	+76 bytes
6	7405 bytes	+136 bytes (+1.87%)	+116 bytes
7	7430 bytes	+161 bytes (+2.21%)	+141 bytes
8	7452 bytes	+183 bytes (+2.52%)	+163 bytes

Non-DEFLATE Algorithms

Archivers based on completely different compression algorithms often produce superior results.
Unfortunately, browsers only support gzip compression at the moment.
However, support for Brotli is constantly growing - for example, your browser actually supports it !

Algorithm	Program	Parameters	Size	Compared To Best Zopfli
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	6541 bytes	-728 bytes (-10.02%)
Brotli (Wikipedia)	brotli	brotli -q 11	6815 bytes	-454 bytes (-6.25%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	6941 bytes	-328 bytes (-4.51%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	7235 bytes	-34 bytes (-0.47%)
LZMA2 (Wikipedia)	xz	xz -9	7252 bytes	-17 bytes (-0.23%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	7259 bytes	-10 bytes (-0.14%)
Zstandard (Wikipedia)	zstd	zstd -19	7263 bytes	-6 bytes (-0.08%)

Detailled Analysis

I wrote a DEFLATE decoder in Javascript. Click the button below to start a client-side analysis of the smallest gzipped files (may take a second):

Load and Parse Data

Notes: pigz is a fast open source multi-threaded implementation of gzip written by one of the original authors of gzip.
However, when using compression level 11, pigz actually switches to the slower Zopfli algorithm and isn't multi-threaded anymore.
KrzyMOD's extensions to Zopfli offer the highest level of configuration and is therefore used for my brute-force search.
Ken Silverman wrote the closed-source KZIP compression program and Jonathon Fowler ported it to Linux.
Defluff was created by Joachim Henke; DeflOpt is a tool by Ben Jos Walbeehm.

website made by Stephan Brumme in 2015 and still improving in 2026.
all timestamps are displayed in central european time. see my changelog.
no flash, not even images or external css files - and everything squeezed into a single html file.
which was handsomely compressed before releasing it into the wild internet - obviously.

please visit my homepage and my blog, too.
email: minime (at) stephan-brumme.com

All trademarks are property of their respective owners. You know, the boring legal stuff.