UnderscoreJS 1.13.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 68420 bytes (66.8k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 19530 bytes (19.1k, 29%).

After GZIP compression these minified files vary in size:

unpkg	8938 bytes (8.7k)	CDN
Boot	7520 bytes (7.3k)	CDN
cdnjs	7520 bytes (7.3k)	CDN
gzip -6 (default)	7517 bytes (7.3k)	local copy
gzip -9	7509 bytes (7.3k)	local copy
libdeflate -12	7326 bytes (7.2k)	local copy
7zip -mx=9 -tgzip	7315 bytes (7.1k)	local copy
kzip -s0 -rn -b2	7313 bytes (7.1k)	local copy
zultra	7312 bytes (7.1k)	local copy
pigz -11 -n	7306 bytes (7.1k)	local copy
Zopfli	7295 bytes (7.1k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.13.1.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.13.1 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 225 bytes by using my UnderscoreJS 1.13.1 Zopfli version instead of the best available CDN (3.08% smaller than cdnjs, 7295 vs. 7520 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 --mls2048 --bsr9 --lazy --ohh

(found July 22, 2021)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	2048	--mls2048
block splitting recursion	9	--bsr9
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/1.13.1/underscore-min.js --location | md5sum
426e8e61dd81d4c6f9c17f1150ad07ce -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.13.1.min.zopfli.js.gz | md5sum
426e8e61dd81d4c6f9c17f1150ad07ce -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.13.1/underscore-min.js --location | sha1sum
bdf0b85756ee2b41ff1e0c86960bf14c740c34ce -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.13.1.min.zopfli.js.gz | sha1sum
bdf0b85756ee2b41ff1e0c86960bf14c740c34ce -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
unpkg	8938 bytes	426e8e61dd81d4c6f9c17f1150ad07ce	(invalid)
Boot	7520 bytes	426e8e61dd81d4c6f9c17f1150ad07ce	(invalid)
cdnjs	7520 bytes	426e8e61dd81d4c6f9c17f1150ad07ce	(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
7295 bytes	-1 byte	zopfli --i100000 --mls2048 --bsr9 --lazy --ohh	July 22, 2021 @ 10:25
7296 bytes	-1 byte	zopfli --i10000 --mls2048 --bsr13 --lazy --ohh	July 21, 2021 @ 16:11
7297 bytes	-1 byte	zopfli --i1000 --mls2048 --bsr30 --lazy --ohh	July 21, 2021 @ 14:32
7298 bytes	-2 bytes	zopfli --i1000 --mls8192 --bsr7 --lazy --ohh	July 21, 2021 @ 14:18
7300 bytes	–	zopfli --i100 --mls8192 --bsr25 --lazy --ohh	July 21, 2021 @ 14:09

If there are multiple parameter sets yielding the same compressed size, only the first one found is shown.

Most recent activity on July 22, 2021 @ 20:14.

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	7307	7307	7307	7307	7307	7298	7306	7309	7307	7298	7299	7299	7296	7296	7296
4	7305	7305	7302	7306	7303	7305	7304	7306	7307	7303	7302	7297	7296	7296	7295
6	7306	7305	7305	7303	7304	7305	7305	7306	7306	7304	7300	7298	7298	7297	7300
7	7302	7302	7305	7302	7302	7303	7303	7300	7306	7298	7299	7298	7297	7297	7297
8	7302	7302	7304	7303	7304	7297	7303	7302	7304	7301	7300	7298	7297	7296	7297
9	7302	7302	7303	7303	7302	7305	7303	7302	7299	7297	7295	7298	7298	7303	7303
10	7309	7305	7310	7305	7312	7297	7298	7299	7301	7301	7299	7298	7303	7297	7298
11	7302	7302	7303	7303	7305	7297	7304	7302	7304	7301	7299	7298	7298	7296	7297
12	7302	7302	7304	7302	7302	7303	7303	7302	7307	7298	7303	7298	7298	7298	7298
13	7302	7305	7304	7303	7304	7303	7306	7306	7298	7298	7295	7298	7298	7297	7296
14	7305	7305	7305	7304	7304	7297	7298	7302	7306	7301	7299	7298	7298	7296	7299
15	7304	7302	7302	7302	7304	7303	7302	7302	7304	7298	7296	7298	7302	7298	7298
16	7304	7305	7303	7305	7304	7303	7304	7305	7299	7301	7295	7298	7298	7298	7297
17	7302	7302	7303	7305	7305	7297	7305	7299	7307	7305	7299	7298	7300	7298	7297
18	7302	7302	7304	7303	7302	7303	7305	7302	7304	7301	7299	7303	7302	7297	7298
19	7304	7305	7306	7302	7303	7302	7303	7302	7297	7297	7297	7298	7302	7298	7298
20	7302	7305	7305	7303	7302	7297	7303	7302	7305	7304	7299	7297	7298	7297	7297
21	7303	7303	7303	7305	7304	7303	7303	7302	7301	7305	7299	7298	7298	7297	7297
22	7302	7302	7303	7303	7304	7303	7303	7302	7297	7297	7299	7298	7298	7298	7297
23	7302	7302	7305	7303	7302	7297	7305	7302	7304	7301	7299	7298	7304	7297	7296
25	7302	7302	7303	7303	7304	7303	7305	7302	7298	7297	7299	7303	7295	7298	7298
30	7304	7303	7302	7303	7305	7303	7302	7302	7304	7301	7295	7298	7295	7299	7298
40	7305	7302	7304	7302	7302	7295	7303	7302	7297	7302	7299	7303	7298	7296	7296

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	7300 bytes	–	100%
1,000	7297 bytes	-3 bytes	100%
10,000	7296 bytes	-1 byte	100%
100,000	7295 bytes	-1 byte	6.09%
1,000,000	7295 bytes	–	2.32%
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)	7314 bytes	+19 bytes (+0.26%)	+1 byte
1	7314 bytes	+19 bytes (+0.26%)	+1 byte
2	7313 bytes	+18 bytes (+0.25%)	–
3	7336 bytes	+41 bytes (+0.56%)	+23 bytes
4	7361 bytes	+66 bytes (+0.90%)	+48 bytes
5	7390 bytes	+95 bytes (+1.30%)	+77 bytes
6	7429 bytes	+134 bytes (+1.84%)	+116 bytes
7	7453 bytes	+158 bytes (+2.17%)	+140 bytes
8	7476 bytes	+181 bytes (+2.48%)	+163 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	6565 bytes	-730 bytes (-10.01%)
Brotli (Wikipedia)	brotli	brotli -q 11	6835 bytes	-460 bytes (-6.31%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	6966 bytes	-329 bytes (-4.51%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	7260 bytes	-35 bytes (-0.48%)
LZMA2 (Wikipedia)	xz	xz -9	7272 bytes	-23 bytes (-0.32%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	7286 bytes	-9 bytes (-0.12%)
Zstandard (Wikipedia)	zstd	zstd -19	7292 bytes	-3 bytes (-0.04%)

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.