UnderscoreJS 0.3.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 15766 bytes (15.4k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 5702 bytes (5.6k, 36%).

After GZIP compression these minified files vary in size:

Boot	2120 bytes (2.1k)	CDN
gzip -9	1940 bytes (1.9k)	local copy
gzip -6 (default)	1939 bytes (1.9k)	local copy
Baidu	1924 bytes (1.9k)	CDN
cdnjs	1924 bytes (1.9k)	CDN
libdeflate -12	1878 bytes (1.8k)	local copy
kzip -s0 -rn -b1	1876 bytes (1.8k)	local copy
zultra	1876 bytes (1.8k)	local copy
7zip -mx=9 -tgzip	1875 bytes (1.8k)	local copy
pigz -11 -n	1874 bytes (1.8k)	local copy
Zopfli	1872 bytes (1.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-0.3.1.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 0.3.1 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 52 bytes by using my UnderscoreJS 0.3.1 Zopfli version instead of the best available CDN (2.78% smaller than cdnjs, 1872 vs. 1924 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 --mls32768 --bsr15 --lazy --ohh

(found February 2, 2016)

Description	Value	Parameter
iterations	10000	--i10000
maximum blocks	8	--mb8
maximum length score	32768	--mls32768
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/0.3.1/underscore-min.js --location | md5sum
3505102f522c71224155d398a97f4fcd -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.3.1.min.zopfli.js.gz | md5sum
3505102f522c71224155d398a97f4fcd -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/0.3.1/underscore-min.js --location | sha1sum
98c6a2becc6211594868fc8f63e40d778bbfd48c -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.3.1.min.zopfli.js.gz | sha1sum
98c6a2becc6211594868fc8f63e40d778bbfd48c -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	2120 bytes	3505102f522c71224155d398a97f4fcd	(invalid)
Baidu	1924 bytes	3505102f522c71224155d398a97f4fcd	(invalid)
cdnjs	1924 bytes	3505102f522c71224155d398a97f4fcd	(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
1872 bytes	-1 byte	zopfli --i10000 --mls32768 --bsr15 --lazy --ohh	February 2, 2016 @ 23:11
1873 bytes	–	zopfli --i100 --mls128 --bsr11 --lazy --ohh	February 2, 2016 @ 20:57

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 @ 12:54.

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:
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	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
4	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
6	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
7	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
8	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
9	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
10	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
11	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
12	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
13	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
14	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
15	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
16	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
17	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
18	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
19	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
20	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
21	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
22	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
23	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
25	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
30	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872
40	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872	1872

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	1873 bytes	–	100%
1,000	1873 bytes	–	100%
10,000	1872 bytes	-1 byte	100%
100,000	1872 bytes	–	100%
1,000,000	1872 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)	1877 bytes	+5 bytes (+0.27%)	+1 byte
1	1876 bytes	+4 bytes (+0.21%)	–
2	1895 bytes	+23 bytes (+1.23%)	+19 bytes
3	1921 bytes	+49 bytes (+2.62%)	+45 bytes
4	1955 bytes	+83 bytes (+4.43%)	+79 bytes
5	1981 bytes	+109 bytes (+5.82%)	+105 bytes
6	2014 bytes	+142 bytes (+7.59%)	+138 bytes
7	2036 bytes	+164 bytes (+8.76%)	+160 bytes
8	2067 bytes	+195 bytes (+10.42%)	+191 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
Brotli (Wikipedia)	brotli	brotli -q 11	1687 bytes	-185 bytes (-9.88%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	1717 bytes	-155 bytes (-8.28%)
Zstandard (Wikipedia)	zstd	zstd -19	1901 bytes	+29 bytes (+1.55%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	1963 bytes	+91 bytes (+4.86%)
LZMA2 (Wikipedia)	xz	xz -9	1968 bytes	+96 bytes (+5.13%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2024 bytes	+152 bytes (+8.12%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	2631 bytes	+759 bytes (+40.54%)

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.