UnderscoreJS 1.2.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 34097 bytes (33.3k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 11887 bytes (11.6k, 35%).

After GZIP compression these minified files vary in size:

Boot	4445 bytes (4.3k)	CDN
Baidu	3999 bytes (3.9k)	CDN
gzip -6 (default)	3986 bytes (3.9k)	local copy
cdnjs	3980 bytes (3.9k)	CDN
gzip -9	3980 bytes (3.9k)	local copy
unpkg	3967 bytes (3.9k)	CDN
libdeflate -12	3890 bytes (3.8k)	local copy
7zip -mx=9 -tgzip	3887 bytes (3.8k)	local copy
kzip -s0 -rn -b1	3884 bytes (3.8k)	local copy
zultra	3876 bytes (3.8k)	local copy
pigz -11 -n	3874 bytes (3.8k)	local copy
Zopfli	3866 bytes (3.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.1.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.2.1 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 101 bytes by using my UnderscoreJS 1.2.1 Zopfli version instead of the best available CDN (2.61% smaller than unpkg, 3866 vs. 3967 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 --i10000 --mb8 --mls512 --bsr12 --lazy --ohh

(found September 8, 2015)

Description	Value	Parameter
iterations	10000	--i10000
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/1.2.1/underscore-min.js --location | md5sum
08d02bde090fcd9ad5e7587838e252d7 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.1.min.zopfli.js.gz | md5sum
08d02bde090fcd9ad5e7587838e252d7 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.2.1/underscore-min.js --location | sha1sum
083bbcd739b7b1336f13c72603e1704b164c02bd -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.1.min.zopfli.js.gz | sha1sum
083bbcd739b7b1336f13c72603e1704b164c02bd -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	4445 bytes	08d02bde090fcd9ad5e7587838e252d7	(invalid)
cdnjs	3980 bytes	08d02bde090fcd9ad5e7587838e252d7	(invalid)
unpkg	3967 bytes	08d02bde090fcd9ad5e7587838e252d7	July 11, 2016 @ 16:49

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	3999 bytes	e6ac0afe8f060689dfe428a4b5965f01	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
3866 bytes	-1 byte	zopfli --i10000 --mls512 --bsr12 --lazy --ohh	September 8, 2015 @ 16:09
3867 bytes	-1 byte	zopfli --i1000 --mls512 --bsr11 --lazy --ohh	September 8, 2015 @ 10:59
3868 bytes	–	zopfli --i100 --mls512 --bsr10 --lazy --ohh	September 8, 2015 @ 10:32

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 @ 12:55.

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	3875	3875	3875	3875	3874	3875	3876	3876	3876	3877	3875	3873	3873	3872	3872
4	3869	3869	3866	3867	3869	3868	3866	3868	3867	3868	3867	3870	3869	3869	3869
6	3868	3868	3868	3870	3869	3869	3869	3870	3866	3867	3870	3868	3869	3870	3870
7	3868	3868	3867	3868	3869	3869	3866	3867	3866	3868	3872	3870	3869	3869	3869
8	3870	3870	3869	3867	3869	3868	3867	3866	3867	3868	3870	3870	3868	3868	3868
9	3870	3870	3868	3867	3867	3867	3868	3869	3867	3868	3867	3867	3869	3869	3869
10	3870	3870	3867	3869	3869	3868	3866	3870	3866	3868	3870	3870	3868	3868	3868
11	3867	3867	3867	3867	3869	3869	3866	3866	3866	3870	3873	3868	3869	3869	3869
12	3870	3870	3867	3867	3869	3869	3868	3868	3866	3870	3873	3868	3869	3869	3869
13	3868	3868	3867	3867	3869	3869	3866	3867	3867	3870	3869	3870	3868	3868	3868
14	3870	3870	3869	3869	3869	3868	3867	3867	3867	3869	3870	3868	3869	3868	3868
15	3867	3867	3867	3869	3869	3869	3866	3867	3867	3869	3873	3870	3869	3869	3869
16	3870	3870	3869	3867	3869	3869	3866	3867	3866	3868	3868	3868	3868	3868	3868
17	3867	3867	3869	3867	3869	3869	3866	3870	3867	3868	3868	3870	3869	3869	3869
18	3870	3870	3869	3868	3869	3869	3866	3868	3867	3867	3872	3868	3868	3868	3868
19	3870	3870	3869	3867	3869	3869	3868	3870	3867	3868	3867	3867	3868	3868	3868
20	3867	3867	3869	3867	3869	3869	3866	3866	3866	3870	3873	3867	3868	3868	3868
21	3870	3870	3869	3867	3869	3869	3866	3870	3866	3870	3868	3867	3870	3868	3868
22	3870	3870	3869	3867	3869	3869	3867	3866	3867	3870	3869	3877	3869	3868	3868
23	3869	3869	3867	3867	3869	3869	3866	3867	3866	3869	3872	3867	3869	3868	3868
25	3867	3867	3869	3867	3869	3868	3870	3868	3867	3869	3870	3867	3868	3868	3868
30	3870	3870	3869	3867	3869	3869	3866	3870	3867	3869	3873	3868	3869	3868	3868
40	3870	3870	3869	3867	3869	3869	3867	3867	3867	3868	3869	3869	3868	3868	3868

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	3868 bytes	–	100%
1,000	3867 bytes	-1 byte	100%
10,000	3866 bytes	-1 byte	100%
100,000	3866 bytes	–	7.83%
1,000,000	3866 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)	3884 bytes	+18 bytes (+0.47%)	–
1	3884 bytes	+18 bytes (+0.47%)	–
2	3899 bytes	+33 bytes (+0.85%)	+15 bytes
3	3894 bytes	+28 bytes (+0.72%)	+10 bytes
4	3918 bytes	+52 bytes (+1.35%)	+34 bytes
5	3942 bytes	+76 bytes (+1.97%)	+58 bytes
6	3974 bytes	+108 bytes (+2.79%)	+90 bytes
7	4008 bytes	+142 bytes (+3.67%)	+124 bytes
8	4041 bytes	+175 bytes (+4.53%)	+157 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	3480 bytes	-386 bytes (-9.98%)
Brotli (Wikipedia)	brotli	brotli -q 11	3561 bytes	-305 bytes (-7.89%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	3853 bytes	-13 bytes (-0.34%)
Zstandard (Wikipedia)	zstd	zstd -19	3901 bytes	+35 bytes (+0.91%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	3934 bytes	+68 bytes (+1.76%)
LZMA2 (Wikipedia)	xz	xz -9	3964 bytes	+98 bytes (+2.53%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	4330 bytes	+464 bytes (+12.00%)

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.