UnderscoreJS 1.10.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 60061 bytes (58.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 17532 bytes (17.1k, 29%).

After GZIP compression these minified files vary in size:

unpkg	7475 bytes (7.3k)	CDN
gzip -6 (default)	6730 bytes (6.6k)	local copy
gzip -9	6728 bytes (6.6k)	local copy
7zip -mx=9 -tgzip	6565 bytes (6.4k)	local copy
libdeflate -12	6562 bytes (6.4k)	local copy
kzip -s0 -rn -b1	6554 bytes (6.4k)	local copy
pigz -11 -n	6554 bytes (6.4k)	local copy
zultra	6553 bytes (6.4k)	local copy
Zopfli	6532 bytes (6.4k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.10.1.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.10.1 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 943 bytes by using my UnderscoreJS 1.10.1 Zopfli version instead of the best available CDN (14.44% smaller than unpkg, 6532 vs. 7475 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 --mls8192 --bsr23 --lazy --ohh

(found May 19, 2020)

Description	Value	Parameter
iterations	1000000	--i1000000
maximum blocks	8	--mb8
maximum length score	8192	--mls8192
block splitting recursion	23	--bsr23
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/1.10.1/underscore-min.js --location | md5sum
6f4bb6d1c719d3607de8cf6d3b4b851f -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.10.1.min.zopfli.js.gz | md5sum
6f4bb6d1c719d3607de8cf6d3b4b851f -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.10.1/underscore-min.js --location | sha1sum
f59e6eb3de8cfb0cf0edd6dcec46fbcac2976bd1 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.10.1.min.zopfli.js.gz | sha1sum
f59e6eb3de8cfb0cf0edd6dcec46fbcac2976bd1 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
unpkg	7475 bytes	6f4bb6d1c719d3607de8cf6d3b4b851f	(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
6532 bytes	-1 byte	zopfli --i1000000 --mls8192 --bsr23 --lazy --ohh	May 19, 2020 @ 22:27
6533 bytes	-1 byte	zopfli --i100000 --mls32768 --bsr18 --lazy --ohh	May 19, 2020 @ 15:29
6534 bytes	-1 byte	zopfli --i10000 --mls32768 --bsr18 --lazy --ohh	May 19, 2020 @ 14:41
6535 bytes	-2 bytes	zopfli --i1000 --mls32768 --bsr18 --lazy --ohh	May 19, 2020 @ 14:36
6537 bytes	–	zopfli --i100 --mls32768 --bsr17 --lazy --ohh	May 19, 2020 @ 14:30

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 @ 12:54.

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	6553	6553	6554	6555	6553	6547	6547	6552	6549	6552	6553	6550	6553	6553	6553
4	6551	6552	6551	6552	6552	6543	6540	6543	6549	6549	6542	6554	6554	6535	6535
6	6544	6545	6550	6549	6549	6550	6548	6549	6549	6548	6543	6534	6554	6536	6536
7	6548	6537	6549	6546	6550	6537	6549	6550	6549	6549	6539	6551	6554	6533	6533
8	6552	6552	6549	6550	6553	6549	6554	6544	6544	6550	6545	6542	6553	6534	6534
9	6547	6554	6549	6546	6552	6542	6550	6550	6549	6549	6543	6537	6536	6534	6534
10	6548	6548	6552	6546	6550	6549	6551	6551	6542	6548	6543	6553	6553	6533	6533
11	6554	6553	6549	6549	6550	6545	6550	6550	6549	6548	6545	6553	6553	6542	6542
12	6555	6555	6555	6554	6537	6537	6540	6550	6549	6548	6549	6539	6553	6533	6533
13	6549	6549	6549	6549	6550	6550	6550	6548	6550	6549	6553	6534	6554	6553	6553
14	6553	6553	6543	6542	6542	6543	6542	6545	6549	6539	6548	6536	6536	6532	6532
15	6548	6548	6549	6549	6550	6539	6549	6550	6549	6549	6539	6551	6533	6553	6553
16	6548	6554	6549	6549	6534	6538	6537	6550	6549	6544	6539	6540	6541	6536	6536
17	6554	6553	6551	6549	6550	6536	6551	6552	6549	6549	6539	6542	6554	6533	6533
18	6548	6548	6548	6550	6552	6537	6537	6545	6549	6548	6545	6537	6553	6533	6533
19	6549	6553	6548	6549	6550	6537	6551	6548	6549	6548	6539	6553	6538	6534	6534
20	6547	6550	6549	6550	6552	6538	6539	6550	6548	6548	6539	6538	6553	6553	6553
21	6554	6554	6551	6549	6550	6550	6551	6550	6549	6543	6554	6541	6539	6539	6539
22	6549	6549	6549	6547	6553	6538	6537	6550	6549	6548	6543	6539	6553	6532	6532
23	6554	6554	6549	6549	6550	6550	6551	6550	6548	6548	6553	6540	6532	6532	6532
25	6554	6554	6549	6552	6550	6538	6549	6550	6549	6548	6546	6535	6553	6534	6534
30	6547	6552	6550	6550	6550	6549	6538	6551	6549	6549	6539	6540	6553	6536	6536
40	6548	6549	6549	6549	6550	6549	6551	6548	6550	6549	6539	6540	6532	6532	6532

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	6537 bytes	–	100%
1,000	6535 bytes	-2 bytes	100%
10,000	6534 bytes	-1 byte	100%
100,000	6533 bytes	-1 byte	10.14%
1,000,000	6532 bytes	-1 byte	6.09%
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)	6554 bytes	+22 bytes (+0.34%)	–
1	6554 bytes	+22 bytes (+0.34%)	–
2	6568 bytes	+36 bytes (+0.55%)	+14 bytes
3	6593 bytes	+61 bytes (+0.93%)	+39 bytes
4	6611 bytes	+79 bytes (+1.21%)	+57 bytes
5	6616 bytes	+84 bytes (+1.29%)	+62 bytes
6	6644 bytes	+112 bytes (+1.71%)	+90 bytes
7	6682 bytes	+150 bytes (+2.30%)	+128 bytes
8	6708 bytes	+176 bytes (+2.69%)	+154 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	5858 bytes	-674 bytes (-10.32%)
Brotli (Wikipedia)	brotli	brotli -q 11	6100 bytes	-432 bytes (-6.61%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	6112 bytes	-420 bytes (-6.43%)
Zstandard (Wikipedia)	zstd	zstd -19	6524 bytes	-8 bytes (-0.12%)
LZMA2 (Wikipedia)	xz	xz -9	6540 bytes	+8 bytes (+0.12%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	6557 bytes	+25 bytes (+0.38%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	6634 bytes	+102 bytes (+1.56%)

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.