UnderscoreJS 1.13.5 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 68416 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 19526 bytes (19.1k, 29%).

After GZIP compression these minified files vary in size:

unpkg	10257 bytes (10.0k)	CDN
Boot	7534 bytes (7.4k)	CDN
cdnjs	7526 bytes (7.3k)	CDN
gzip -6 (default)	7519 bytes (7.3k)	local copy
gzip -9	7510 bytes (7.3k)	local copy
libdeflate -12	7332 bytes (7.2k)	local copy
zultra	7321 bytes (7.1k)	local copy
7zip -mx=9 -tgzip	7319 bytes (7.1k)	local copy
kzip -s0 -rn -b2	7319 bytes (7.1k)	local copy
pigz -11 -n	7317 bytes (7.1k)	local copy
Zopfli	7302 bytes (7.1k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.13.5.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.13.5 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 224 bytes by using my UnderscoreJS 1.13.5 Zopfli version instead of the best available CDN (3.07% smaller than cdnjs, 7302 vs. 7526 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 --bsr30 --lazy --ohh

(found September 26, 2022)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	2048	--mls2048
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/1.13.5/underscore-min.js --location | md5sum
f6dcb96fbc6532ba3be28c1fde27998a -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.13.5.min.zopfli.js.gz | md5sum
f6dcb96fbc6532ba3be28c1fde27998a -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.13.5/underscore-min.js --location | sha1sum
3c45792a1111d71a34f42bbda6764619afd36d40 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.13.5.min.zopfli.js.gz | sha1sum
3c45792a1111d71a34f42bbda6764619afd36d40 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
unpkg	10257 bytes	f6dcb96fbc6532ba3be28c1fde27998a	(invalid)
Boot	7534 bytes	f6dcb96fbc6532ba3be28c1fde27998a	September 26, 2022 @ 14:51
cdnjs	7526 bytes	f6dcb96fbc6532ba3be28c1fde27998a	(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
7302 bytes	-1 byte	zopfli --i100000 --mls2048 --bsr30 --lazy --ohh	September 26, 2022 @ 18:03
7303 bytes	-1 byte	zopfli --i10000 --mls2048 --bsr30 --lazy --ohh	September 26, 2022 @ 17:55
7304 bytes	-1 byte	zopfli --i1000 --mls2048 --bsr30 --lazy --ohh	September 26, 2022 @ 17:54
7305 bytes	-2 bytes	zopfli --i1000 --mls2048 --bsr22 --lazy --ohh	September 26, 2022 @ 17:54
7307 bytes	–	zopfli --i100 --mls2048 --bsr16 --lazy --ohh	September 26, 2022 @ 14:52

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

Most recent activity on September 26, 2022 @ 20:16.

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 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	7313	7313	7314	7314	7314	7306	7306	7314	7306	7306	7306	7307	7304	7306	7306
4	7310	7310	7310	7311	7307	7310	7310	7312	7312	7312	7305	7304	7306	7306	7306
6	7312	7309	7310	7309	7307	7310	7309	7311	7310	7309	7305	7306	7306	7306	7306
7	7311	7312	7308	7309	7308	7309	7310	7311	7311	7304	7305	7306	7306	7306	7306
8	7310	7313	7310	7312	7308	7306	7305	7311	7307	7309	7306	7307	7306	7306	7306
9	7310	7314	7310	7310	7311	7310	7310	7311	7308	7308	7304	7306	7306	7306	7311
10	7311	7307	7310	7310	7311	7309	7311	7310	7310	7307	7304	7306	7307	7306	7306
11	7307	7308	7310	7311	7311	7307	7311	7311	7310	7308	7304	7307	7306	7311	7306
12	7311	7307	7310	7310	7311	7310	7311	7311	7306	7304	7305	7311	7306	7306	7306
13	7310	7313	7308	7309	7307	7309	7309	7311	7310	7308	7304	7308	7306	7306	7306
14	7309	7307	7309	7311	7311	7306	7304	7311	7310	7309	7305	7312	7306	7306	7306
15	7312	7308	7309	7310	7311	7309	7310	7311	7309	7305	7304	7307	7306	7306	7306
16	7312	7308	7310	7310	7308	7310	7311	7311	7308	7309	7304	7305	7306	7306	7306
17	7308	7308	7310	7310	7308	7310	7310	7307	7306	7309	7304	7306	7306	7306	7306
18	7311	7308	7309	7311	7311	7308	7310	7306	7309	7307	7304	7306	7306	7306	7306
19	7308	7308	7309	7310	7311	7311	7311	7311	7310	7310	7304	7305	7306	7306	7306
20	7308	7307	7310	7309	7308	7310	7310	7309	7306	7307	7306	7306	7306	7306	7306
21	7310	7308	7308	7311	7308	7311	7310	7311	7309	7309	7304	7305	7311	7306	7306
22	7308	7308	7308	7309	7307	7309	7310	7309	7309	7307	7304	7306	7306	7306	7306
23	7308	7308	7310	7309	7309	7310	7310	7311	7308	7309	7304	7305	7306	7306	7306
25	7310	7313	7310	7309	7308	7310	7310	7309	7312	7306	7304	7306	7306	7306	7306
30	7312	7312	7309	7310	7311	7311	7311	7310	7309	7307	7302	7304	7306	7306	7306
40	7310	7312	7309	7311	7311	7308	7311	7311	7310	7304	7302	7304	7306	7306	7306

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	7307 bytes	–	100%
1,000	7304 bytes	-3 bytes	100%
10,000	7303 bytes	-1 byte	100%
100,000	7302 bytes	-1 byte	0.58%
1,000,000	7302 bytes	–	0.58%
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)	7319 bytes	+17 bytes (+0.23%)	–
1	7323 bytes	+21 bytes (+0.29%)	+4 bytes
2	7319 bytes	+17 bytes (+0.23%)	–
3	7339 bytes	+37 bytes (+0.51%)	+20 bytes
4	7369 bytes	+67 bytes (+0.92%)	+50 bytes
5	7394 bytes	+92 bytes (+1.26%)	+75 bytes
6	7429 bytes	+127 bytes (+1.74%)	+110 bytes
7	7456 bytes	+154 bytes (+2.11%)	+137 bytes
8	7477 bytes	+175 bytes (+2.40%)	+158 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	6566 bytes	-736 bytes (-10.08%)
Brotli (Wikipedia)	brotli	brotli -q 11	6844 bytes	-458 bytes (-6.27%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	6961 bytes	-341 bytes (-4.67%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	7234 bytes	-68 bytes (-0.93%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	7276 bytes	-26 bytes (-0.36%)
LZMA2 (Wikipedia)	xz	xz -9	7284 bytes	-18 bytes (-0.25%)
Zstandard (Wikipedia)	zstd	zstd -19	7298 bytes	-4 bytes (-0.05%)

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.