UnderscoreJS 0.3.2 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 15699 bytes (15.3k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 5688 bytes (5.6k, 36%).

After GZIP compression these minified files vary in size:

Boot	2105 bytes (2.1k)	CDN
gzip -9	1927 bytes (1.9k)	local copy
gzip -6 (default)	1924 bytes (1.9k)	local copy
Baidu	1911 bytes (1.9k)	CDN
cdnjs	1911 bytes (1.9k)	CDN
libdeflate -12	1866 bytes (1.8k)	local copy
kzip -s0 -rn -b1	1865 bytes (1.8k)	local copy
pigz -11 -n	1863 bytes (1.8k)	local copy
zultra	1863 bytes (1.8k)	local copy
7zip -mx=9 -tgzip	1861 bytes (1.8k)	local copy
Zopfli	1860 bytes (1.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-0.3.2.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 0.3.2 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 51 bytes by using my UnderscoreJS 0.3.2 Zopfli version instead of the best available CDN (2.74% smaller than cdnjs, 1860 vs. 1911 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 --i1000000 --mb8 --mls32 --bsr17 --lazy --ohh

(found March 4, 2020)

Description	Value	Parameter
iterations	1000000	--i1000000
maximum blocks	8	--mb8
maximum length score	32	--mls32
block splitting recursion	17	--bsr17
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/0.3.2/underscore-min.js --location | md5sum
2906bd885102a6cd0b116bf96580b00d -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.3.2.min.zopfli.js.gz | md5sum
2906bd885102a6cd0b116bf96580b00d -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/0.3.2/underscore-min.js --location | sha1sum
33aa9b1cda80a8c9d7043c987bfa7ee2002ba794 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.3.2.min.zopfli.js.gz | sha1sum
33aa9b1cda80a8c9d7043c987bfa7ee2002ba794 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	2105 bytes	2906bd885102a6cd0b116bf96580b00d	(invalid)
Baidu	1911 bytes	2906bd885102a6cd0b116bf96580b00d	(invalid)
cdnjs	1911 bytes	2906bd885102a6cd0b116bf96580b00d	(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
1860 bytes	-1 byte	zopfli --i1000000 --mls32 --bsr17 --lazy --ohh	March 4, 2020 @ 12:57
1861 bytes	–	zopfli --i100 --mls32 --bsr7 --lazy --ohh	February 2, 2016 @ 20:59

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	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
4	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
6	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
7	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
8	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
9	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
10	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
11	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
12	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
13	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
14	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
15	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
16	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
17	1861	1861	1861	1861	1860	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
18	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
19	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
20	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
21	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
22	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
23	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
25	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
30	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861
40	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861	1861

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	1861 bytes	–	100%
1,000	1861 bytes	–	100%
10,000	1861 bytes	–	100%
100,000	1861 bytes	–	100%
1,000,000	1860 bytes	-1 byte	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)	1865 bytes	+5 bytes (+0.27%)	–
1	1865 bytes	+5 bytes (+0.27%)	–
2	1883 bytes	+23 bytes (+1.24%)	+18 bytes
3	1910 bytes	+50 bytes (+2.69%)	+45 bytes
4	1945 bytes	+85 bytes (+4.57%)	+80 bytes
5	1977 bytes	+117 bytes (+6.29%)	+112 bytes
6	1998 bytes	+138 bytes (+7.42%)	+133 bytes
7	2032 bytes	+172 bytes (+9.25%)	+167 bytes
8	2057 bytes	+197 bytes (+10.59%)	+192 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	1680 bytes	-180 bytes (-9.68%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	1708 bytes	-152 bytes (-8.17%)
Zstandard (Wikipedia)	zstd	zstd -19	1891 bytes	+31 bytes (+1.67%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	1949 bytes	+89 bytes (+4.78%)
LZMA2 (Wikipedia)	xz	xz -9	1956 bytes	+96 bytes (+5.16%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2012 bytes	+152 bytes (+8.17%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	2618 bytes	+758 bytes (+40.75%)

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.