UnderscoreJS 0.3.3 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 16400 bytes (16.0k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 5982 bytes (5.8k, 36%).

After GZIP compression these minified files vary in size:

Boot	2192 bytes (2.1k)	CDN
gzip -6 (default)	2002 bytes (2.0k)	local copy
gzip -9	2002 bytes (2.0k)	local copy
Baidu	1985 bytes (1.9k)	CDN
cdnjs	1985 bytes (1.9k)	CDN
libdeflate -12	1941 bytes (1.9k)	local copy
kzip -s0 -rn -b1	1938 bytes (1.9k)	local copy
pigz -11 -n	1938 bytes (1.9k)	local copy
7zip -mx=9 -tgzip	1937 bytes (1.9k)	local copy
zultra	1937 bytes (1.9k)	local copy
Zopfli	1935 bytes (1.9k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-0.3.3.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 0.3.3 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 50 bytes by using my UnderscoreJS 0.3.3 Zopfli version instead of the best available CDN (2.58% smaller than cdnjs, 1935 vs. 1985 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 --i1000 --mb8 --mls512 --bsr2 --lazy --ohh

(found February 2, 2016)

Description	Value	Parameter
iterations	1000	--i1000
maximum blocks	8	--mb8
maximum length score	512	--mls512
block splitting recursion	2	--bsr2
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/0.3.3/underscore-min.js --location | md5sum
1e05fc11b907519a5c1d6546cc036217 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.3.3.min.zopfli.js.gz | md5sum
1e05fc11b907519a5c1d6546cc036217 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/0.3.3/underscore-min.js --location | sha1sum
db5bd7f83bb9e0828832bf45f68509443263141f -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.3.3.min.zopfli.js.gz | sha1sum
db5bd7f83bb9e0828832bf45f68509443263141f -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	2192 bytes	1e05fc11b907519a5c1d6546cc036217	(invalid)
Baidu	1985 bytes	1e05fc11b907519a5c1d6546cc036217	(invalid)
cdnjs	1985 bytes	1e05fc11b907519a5c1d6546cc036217	(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
1935 bytes	-2 bytes	zopfli --i1000 --mls512 --bsr2 --lazy --ohh	February 2, 2016 @ 20:59
1937 bytes	–	zopfli --i100 --mls128 --bsr7 --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 @ 12:55.

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:
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	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
4	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
6	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
7	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
8	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
9	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
10	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
11	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
12	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
13	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
14	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
15	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
16	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
17	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
18	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
19	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
20	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
21	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
22	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
23	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
25	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
30	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935
40	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935	1935

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	1936 bytes	–	100%
1,000	1935 bytes	-1 byte	100%
10,000	1935 bytes	–	100%
100,000	1935 bytes	–	100%
1,000,000	1935 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)	1938 bytes	+3 bytes (+0.16%)	–
1	1938 bytes	+3 bytes (+0.16%)	–
2	1960 bytes	+25 bytes (+1.29%)	+22 bytes
3	1985 bytes	+50 bytes (+2.58%)	+47 bytes
4	2017 bytes	+82 bytes (+4.24%)	+79 bytes
5	2052 bytes	+117 bytes (+6.05%)	+114 bytes
6	2074 bytes	+139 bytes (+7.18%)	+136 bytes
7	2098 bytes	+163 bytes (+8.42%)	+160 bytes
8	2132 bytes	+197 bytes (+10.18%)	+194 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	1744 bytes	-191 bytes (-9.87%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	1768 bytes	-167 bytes (-8.63%)
Zstandard (Wikipedia)	zstd	zstd -19	1965 bytes	+30 bytes (+1.55%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2023 bytes	+88 bytes (+4.55%)
LZMA2 (Wikipedia)	xz	xz -9	2028 bytes	+93 bytes (+4.81%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2063 bytes	+128 bytes (+6.61%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	2675 bytes	+740 bytes (+38.24%)

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.