UnderscoreJS 1.3.2 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 37382 bytes (36.5k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 12815 bytes (12.5k, 34%).

After GZIP compression these minified files vary in size:

Boot	4901 bytes (4.8k)	CDN
Baidu	4415 bytes (4.3k)	CDN
gzip -6 (default)	4406 bytes (4.3k)	local copy
gzip -9	4397 bytes (4.3k)	local copy
cdnjs	4392 bytes (4.3k)	CDN
unpkg	4391 bytes (4.3k)	CDN
libdeflate -12	4279 bytes (4.2k)	local copy
7zip -mx=9 -tgzip	4277 bytes (4.2k)	local copy
zultra	4275 bytes (4.2k)	local copy
kzip -s0 -rn -b0	4274 bytes (4.2k)	local copy
pigz -11 -n	4262 bytes (4.2k)	local copy
Zopfli	4256 bytes (4.2k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.3.2.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.3.2 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 135 bytes by using my UnderscoreJS 1.3.2 Zopfli version instead of the best available CDN (3.17% smaller than unpkg, 4256 vs. 4391 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 --mls512 --bsr11 --lazy --ohh

(found February 8, 2019)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	512	--mls512
block splitting recursion	11	--bsr11
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/1.3.2/underscore-min.js --location | md5sum
a36fc61e8437815d62c58c520117a872 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.3.2.min.zopfli.js.gz | md5sum
a36fc61e8437815d62c58c520117a872 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.3.2/underscore-min.js --location | sha1sum
ede1d022640f26eaa6109da9e924670f6ed14cce -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.3.2.min.zopfli.js.gz | sha1sum
ede1d022640f26eaa6109da9e924670f6ed14cce -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	4901 bytes	a36fc61e8437815d62c58c520117a872	(invalid)
cdnjs	4392 bytes	a36fc61e8437815d62c58c520117a872	(invalid)
unpkg	4391 bytes	a36fc61e8437815d62c58c520117a872	July 11, 2016 @ 16:49

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	4415 bytes	b00b6a74b64a686c2ae9a07dc38565ee	only whitespaces differ	(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
4256 bytes	-2 bytes	zopfli --i100000 --mls512 --bsr11 --lazy --ohh	February 8, 2019 @ 15:57
4258 bytes	-1 byte	zopfli --i10000 --mls512 --bsr11 --lazy --ohh	September 8, 2015 @ 15:13
4259 bytes	-2 bytes	zopfli --i1000 --mls512 --bsr11 --lazy --ohh	September 8, 2015 @ 10:54
4261 bytes	–	zopfli --i100 --mls2048 --bsr6 --lazy --ohh	September 8, 2015 @ 10:34

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

Most recent activity on July 20, 2020 @ 12:52.

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	4267	4266	4267	4266	4266	4274	4274	4261	4274	4266	4267	4266	4267	4266	4266
4	4261	4261	4261	4261	4258	4256	4261	4257	4261	4259	4257	4257	4260	4260	4260
6	4260	4260	4260	4260	4260	4260	4261	4257	4261	4260	4259	4259	4257	4259	4259
7	4272	4272	4273	4273	4257	4260	4260	4256	4256	4260	4259	4259	4259	4259	4259
8	4260	4256	4257	4257	4259	4260	4259	4257	4257	4259	4259	4257	4257	4257	4257
9	4260	4261	4261	4261	4259	4258	4257	4256	4256	4256	4259	4257	4257	4261	4261
10	4256	4259	4261	4261	4260	4260	4259	4256	4256	4260	4259	4259	4259	4259	4259
11	4273	4273	4272	4273	4262	4273	4259	4256	4256	4256	4259	4259	4259	4259	4259
12	4257	4262	4261	4261	4260	4260	4259	4259	4257	4260	4259	4257	4259	4259	4259
13	4260	4260	4257	4260	4260	4260	4260	4264	4257	4260	4259	4259	4257	4257	4257
14	4260	4261	4257	4261	4260	4260	4261	4256	4257	4260	4257	4259	4257	4257	4257
15	4260	4256	4262	4261	4259	4260	4260	4256	4257	4260	4259	4257	4257	4259	4259
16	4259	4260	4262	4261	4257	4260	4260	4256	4257	4260	4257	4257	4257	4257	4257
17	4261	4261	4257	4261	4260	4260	4261	4259	4259	4260	4257	4257	4257	4257	4257
18	4256	4262	4262	4261	4260	4260	4260	4257	4257	4260	4259	4259	4259	4259	4259
19	4256	4261	4258	4257	4257	4260	4259	4256	4256	4259	4259	4259	4259	4259	4259
20	4256	4259	4257	4261	4260	4260	4259	4259	4259	4260	4259	4259	4259	4259	4259
21	4274	4273	4257	4261	4260	4261	4260	4256	4261	4260	4259	4259	4259	4259	4259
22	4260	4261	4257	4257	4260	4260	4259	4256	4256	4260	4259	4259	4259	4259	4259
23	4256	4260	4257	4261	4260	4260	4259	4256	4256	4260	4259	4259	4259	4259	4259
25	4261	4261	4259	4261	4259	4260	4258	4257	4257	4259	4259	4259	4259	4259	4259
30	4259	4261	4258	4261	4259	4258	4261	4262	4259	4260	4257	4257	4259	4259	4259
40	4257	4261	4263	4257	4260	4258	4260	4256	4259	4260	4257	4257	4257	4257	4257

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	4261 bytes	–	100%
1,000	4259 bytes	-2 bytes	100%
10,000	4258 bytes	-1 byte	100%
100,000	4256 bytes	-2 bytes	29.86%
1,000,000	4256 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)	4274 bytes	+18 bytes (+0.42%)	–
1	4274 bytes	+18 bytes (+0.42%)	–
2	4286 bytes	+30 bytes (+0.70%)	+12 bytes
3	4286 bytes	+30 bytes (+0.70%)	+12 bytes
4	4319 bytes	+63 bytes (+1.48%)	+45 bytes
5	4340 bytes	+84 bytes (+1.97%)	+66 bytes
6	4372 bytes	+116 bytes (+2.73%)	+98 bytes
7	4393 bytes	+137 bytes (+3.22%)	+119 bytes
8	4421 bytes	+165 bytes (+3.88%)	+147 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	3805 bytes	-451 bytes (-10.60%)
Brotli (Wikipedia)	brotli	brotli -q 11	3931 bytes	-325 bytes (-7.64%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	4235 bytes	-21 bytes (-0.49%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	4281 bytes	+25 bytes (+0.59%)
Zstandard (Wikipedia)	zstd	zstd -19	4300 bytes	+44 bytes (+1.03%)
LZMA2 (Wikipedia)	xz	xz -9	4348 bytes	+92 bytes (+2.16%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	4635 bytes	+379 bytes (+8.91%)

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.