UnderscoreJS 1.5.2 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 43568 bytes (42.5k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 14358 bytes (14.0k, 33%).

After GZIP compression these minified files vary in size:

Boot	5580 bytes (5.4k)	CDN
jsdelivr	5580 bytes (5.4k)	CDN
gzip -6 (default)	4993 bytes (4.9k)	local copy
Baidu	4989 bytes (4.9k)	CDN
cdnjs	4984 bytes (4.9k)	CDN
gzip -9	4982 bytes (4.9k)	local copy
unpkg	4979 bytes (4.9k)	CDN
Yandex	4960 bytes (4.8k)	CDN
zultra	4867 bytes (4.8k)	local copy
7zip -mx=9 -tgzip	4864 bytes (4.8k)	local copy
libdeflate -12	4859 bytes (4.7k)	local copy
kzip -s0 -rn -b0	4856 bytes (4.7k)	local copy
pigz -11 -n	4847 bytes (4.7k)	local copy
Zopfli	4842 bytes (4.7k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.5.2.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.5.2 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 118 bytes by using my UnderscoreJS 1.5.2 Zopfli version instead of the best available CDN (2.44% smaller than Yandex, 4842 vs. 4960 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 --bsr12 --lazy --ohh

(found September 9, 2015)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	512	--mls512
block splitting recursion	12	--bsr12
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/1.5.2/underscore-min.js --location | md5sum
ca26dc8cdf5d413cd8d3b62490e28210 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.5.2.min.zopfli.js.gz | md5sum
ca26dc8cdf5d413cd8d3b62490e28210 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.5.2/underscore-min.js --location | sha1sum
005cbdf96df45798aec80ada6afd7a6f58652181 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.5.2.min.zopfli.js.gz | sha1sum
005cbdf96df45798aec80ada6afd7a6f58652181 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	5580 bytes	ca26dc8cdf5d413cd8d3b62490e28210	(invalid)
jsdelivr	5580 bytes	ca26dc8cdf5d413cd8d3b62490e28210	(invalid)
cdnjs	4984 bytes	ca26dc8cdf5d413cd8d3b62490e28210	(invalid)
unpkg	4979 bytes	ca26dc8cdf5d413cd8d3b62490e28210	July 11, 2016 @ 16:49
Yandex	4960 bytes	ca26dc8cdf5d413cd8d3b62490e28210	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	4989 bytes	f1b6a32d917945b051781a58a6975af2	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
4842 bytes	-1 byte	zopfli --i100000 --mls512 --bsr12 --lazy --ohh	September 9, 2015 @ 07:27
4843 bytes	–	zopfli --i100 --mls512 --bsr9 --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 @ 12:49.

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	4856	4856	4843	4844	4844	4843	4843	4843	4843	4842	4843	4855	4855	4843	4843
4	4843	4843	4843	4843	4843	4843	4842	4848	4842	4843	4843	4844	4844	4845	4845
6	4844	4844	4843	4844	4844	4843	4843	4844	4843	4843	4843	4843	4843	4843	4843
7	4845	4845	4843	4843	4843	4843	4843	4846	4843	4843	4843	4844	4846	4846	4846
8	4843	4843	4844	4844	4844	4843	4843	4844	4843	4842	4843	4843	4842	4844	4844
9	4844	4844	4843	4844	4844	4843	4844	4844	4842	4843	4842	4843	4843	4845	4845
10	4844	4844	4843	4844	4843	4843	4843	4843	4842	4843	4843	4843	4842	4844	4844
11	4844	4844	4843	4843	4843	4843	4843	4844	4842	4842	4843	4842	4843	4844	4844
12	4844	4844	4843	4843	4843	4843	4843	4844	4842	4844	4842	4844	4844	4844	4844
13	4844	4844	4844	4844	4844	4843	4844	4844	4844	4842	4842	4843	4843	4844	4844
14	4843	4843	4843	4843	4844	4843	4842	4843	4842	4842	4843	4843	4843	4844	4844
15	4844	4844	4843	4843	4843	4843	4843	4844	4844	4843	4844	4844	4846	4844	4844
16	4844	4844	4843	4843	4844	4844	4843	4844	4842	4842	4844	4843	4842	4844	4844
17	4844	4844	4843	4844	4843	4844	4844	4843	4843	4843	4844	4844	4843	4843	4843
18	4844	4844	4843	4844	4847	4847	4843	4843	4843	4843	4844	4843	4844	4844	4844
19	4844	4844	4843	4843	4844	4843	4843	4846	4843	4844	4843	4844	4843	4843	4843
20	4844	4844	4844	4843	4843	4843	4844	4843	4843	4844	4844	4845	4844	4844	4844
21	4844	4844	4843	4843	4844	4845	4844	4844	4843	4843	4844	4845	4843	4844	4844
22	4844	4844	4843	4843	4844	4843	4843	4843	4843	4843	4843	4845	4844	4844	4844
23	4844	4844	4843	4844	4844	4847	4847	4846	4843	4845	4844	4844	4843	4843	4843
25	4845	4845	4844	4843	4844	4843	4842	4843	4844	4843	4844	4844	4844	4844	4844
30	4844	4844	4843	4844	4844	4844	4843	4843	4844	4843	4844	4844	4844	4843	4843
40	4844	4844	4844	4843	4844	4843	4843	4844	4844	4843	4844	4844	4844	4843	4843

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	4843 bytes	–	100%
1,000	4843 bytes	–	100%
10,000	4842 bytes	-1 byte	100%
100,000	4842 bytes	–	15.65%
1,000,000	4842 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)	4856 bytes	+14 bytes (+0.29%)	–
1	4856 bytes	+14 bytes (+0.29%)	–
2	4875 bytes	+33 bytes (+0.68%)	+19 bytes
3	4872 bytes	+30 bytes (+0.62%)	+16 bytes
4	4903 bytes	+61 bytes (+1.26%)	+47 bytes
5	4941 bytes	+99 bytes (+2.04%)	+85 bytes
6	4974 bytes	+132 bytes (+2.73%)	+118 bytes
7	5015 bytes	+173 bytes (+3.57%)	+159 bytes
8	5046 bytes	+204 bytes (+4.21%)	+190 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	4304 bytes	-538 bytes (-11.11%)
Brotli (Wikipedia)	brotli	brotli -q 11	4514 bytes	-328 bytes (-6.77%)
Zstandard (Wikipedia)	zstd	zstd -19	4855 bytes	+13 bytes (+0.27%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	4861 bytes	+19 bytes (+0.39%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	4871 bytes	+29 bytes (+0.60%)
LZMA2 (Wikipedia)	xz	xz -9	4920 bytes	+78 bytes (+1.61%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	5147 bytes	+305 bytes (+6.30%)

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.