UnderscoreJS 0.5.7 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 22692 bytes (22.2k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 8359 bytes (8.2k, 37%).

After GZIP compression these minified files vary in size:

Boot	3051 bytes (3.0k)	CDN
gzip -6 (default)	2754 bytes (2.7k)	local copy
gzip -9	2753 bytes (2.7k)	local copy
Baidu	2751 bytes (2.7k)	CDN
cdnjs	2738 bytes (2.7k)	CDN
7zip -mx=9 -tgzip	2677 bytes (2.6k)	local copy
zultra	2676 bytes (2.6k)	local copy
libdeflate -12	2675 bytes (2.6k)	local copy
pigz -11 -n	2672 bytes (2.6k)	local copy
kzip -s0 -rn -b1	2671 bytes (2.6k)	local copy
Zopfli	2667 bytes (2.6k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-0.5.7.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 0.5.7 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 71 bytes by using my UnderscoreJS 0.5.7 Zopfli version instead of the best available CDN (2.66% smaller than cdnjs, 2667 vs. 2738 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 --mls4096 --bsr30 --lazy --ohh

(found February 3, 2016)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	4096	--mls4096
block splitting recursion	30	--bsr30
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/0.5.7/underscore-min.js --location | md5sum
bddb511fbd4a54c1b77d7a26b8460c89 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.5.7.min.zopfli.js.gz | md5sum
bddb511fbd4a54c1b77d7a26b8460c89 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/0.5.7/underscore-min.js --location | sha1sum
34deaf3d4c79373b1921429f08843fb6a9f032e5 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.5.7.min.zopfli.js.gz | sha1sum
34deaf3d4c79373b1921429f08843fb6a9f032e5 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	3051 bytes	bddb511fbd4a54c1b77d7a26b8460c89	(invalid)
cdnjs	2738 bytes	bddb511fbd4a54c1b77d7a26b8460c89	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	2751 bytes	f4660dfb14a2433de87a681e88400ce4	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
2667 bytes	-1 byte	zopfli --i100000 --mls4096 --bsr30 --lazy --ohh	February 3, 2016 @ 08:32
2668 bytes	-1 byte	zopfli --i10000 --mls4096 --bsr30 --lazy --ohh	February 2, 2016 @ 23:13
2669 bytes	-1 byte	zopfli --i10000 --mls2 --bsr20 --lazy --ohh	February 2, 2016 @ 23:10
2670 bytes	-1 byte	zopfli --i1000 --mls4096 --bsr18 --lazy --ohh	February 2, 2016 @ 21:02
2671 bytes	–	zopfli --i100 --mls8192 --bsr8 --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:
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	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
4	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
6	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
7	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
8	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
9	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
10	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
11	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
12	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
13	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
14	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
15	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
16	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
17	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
18	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
19	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
20	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
21	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
22	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
23	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
25	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
30	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670
40	2669	2669	2669	2670	2669	2670	2670	2670	2670	2670	2670	2667	2670	2670	2670

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	2671 bytes	–	100%
1,000	2670 bytes	-1 byte	100%
10,000	2668 bytes	-2 bytes	100%
100,000	2667 bytes	-1 byte	6.67%
1,000,000	2667 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)	2671 bytes	+4 bytes (+0.15%)	–
1	2671 bytes	+4 bytes (+0.15%)	–
2	2695 bytes	+28 bytes (+1.05%)	+24 bytes
3	2728 bytes	+61 bytes (+2.29%)	+57 bytes
4	2740 bytes	+73 bytes (+2.74%)	+69 bytes
5	2766 bytes	+99 bytes (+3.71%)	+95 bytes
6	2797 bytes	+130 bytes (+4.87%)	+126 bytes
7	2834 bytes	+167 bytes (+6.26%)	+163 bytes
8	2869 bytes	+202 bytes (+7.57%)	+198 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	2397 bytes	-270 bytes (-10.12%)
Brotli (Wikipedia)	brotli	brotli -q 11	2462 bytes	-205 bytes (-7.69%)
Zstandard (Wikipedia)	zstd	zstd -19	2684 bytes	+17 bytes (+0.64%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2722 bytes	+55 bytes (+2.06%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2745 bytes	+78 bytes (+2.92%)
LZMA2 (Wikipedia)	xz	xz -9	2768 bytes	+101 bytes (+3.79%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3290 bytes	+623 bytes (+23.36%)

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.