UnderscoreJS 1.1.5 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 27738 bytes (27.1k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 9963 bytes (9.7k, 36%).

After GZIP compression these minified files vary in size:

Boot	3757 bytes (3.7k)	CDN
Baidu	3408 bytes (3.3k)	CDN
gzip -6 (default)	3406 bytes (3.3k)	local copy
gzip -9	3404 bytes (3.3k)	local copy
cdnjs	3394 bytes (3.3k)	CDN
libdeflate -12	3315 bytes (3.2k)	local copy
7zip -mx=9 -tgzip	3312 bytes (3.2k)	local copy
kzip -s0 -rn -b0	3310 bytes (3.2k)	local copy
pigz -11 -n	3303 bytes (3.2k)	local copy
zultra	3301 bytes (3.2k)	local copy
Zopfli	3298 bytes (3.2k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.5.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.1.5 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 96 bytes by using my UnderscoreJS 1.1.5 Zopfli version instead of the best available CDN (2.91% smaller than cdnjs, 3298 vs. 3394 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 --bsr20 --lazy --ohh

(found February 12, 2019)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	2048	--mls2048
block splitting recursion	20	--bsr20
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/1.1.5/underscore-min.js --location | md5sum
21619893ce1bc4029f11c1c6ec1ecabf -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.5.min.zopfli.js.gz | md5sum
21619893ce1bc4029f11c1c6ec1ecabf -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.1.5/underscore-min.js --location | sha1sum
f665459959c5167c0905974a62ffe923f2c19813 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.1.5.min.zopfli.js.gz | sha1sum
f665459959c5167c0905974a62ffe923f2c19813 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	3757 bytes	21619893ce1bc4029f11c1c6ec1ecabf	(invalid)
cdnjs	3394 bytes	21619893ce1bc4029f11c1c6ec1ecabf	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	3408 bytes	d7fc74b91595fdb53ef9c47fdd955802	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
3298 bytes	-1 byte	zopfli --i100000 --mls2048 --bsr20 --lazy --ohh	February 12, 2019 @ 12:40
3299 bytes	–	zopfli --i100 --mls512 --bsr40 --lazy --ohh	February 2, 2016 @ 19:07

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 @ 12:52.

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	3299	3299	3298	3299	3300	3300	3311	3300	3300	3300	3300	3301	3301	3301	3301
4	3301	3301	3300	3300	3301	3302	3301	3302	3301	3304	3301	3300	3300	3300	3300
6	3302	3302	3301	3301	3300	3301	3301	3300	3301	3304	3298	3301	3299	3299	3299
7	3300	3300	3306	3300	3300	3301	3301	3299	3299	3299	3301	3300	3299	3299	3299
8	3300	3300	3306	3299	3300	3300	3307	3300	3300	3300	3300	3302	3299	3299	3299
9	3300	3300	3300	3300	3300	3300	3300	3299	3301	3301	3304	3300	3299	3299	3299
10	3302	3302	3302	3300	3300	3300	3301	3300	3299	3304	3301	3300	3301	3298	3298
11	3302	3302	3302	3300	3300	3311	3300	3301	3299	3298	3298	3301	3299	3299	3299
12	3300	3300	3302	3300	3300	3301	3300	3302	3299	3301	3301	3300	3299	3299	3299
13	3299	3299	3302	3300	3300	3300	3301	3301	3299	3304	3298	3301	3299	3298	3298
14	3300	3300	3300	3300	3300	3300	3300	3300	3301	3298	3302	3300	3299	3298	3298
15	3307	3307	3306	3300	3300	3308	3301	3301	3299	3301	3298	3301	3301	3298	3298
16	3302	3302	3300	3300	3300	3300	3301	3300	3299	3301	3302	3301	3299	3299	3299
17	3301	3301	3302	3300	3300	3300	3300	3301	3299	3301	3298	3300	3301	3298	3298
18	3301	3301	3307	3299	3300	3299	3300	3301	3299	3304	3303	3301	3299	3298	3298
19	3300	3300	3301	3300	3300	3299	3301	3300	3299	3304	3298	3300	3299	3298	3298
20	3300	3300	3301	3300	3300	3300	3301	3301	3299	3304	3298	3301	3299	3299	3299
21	3300	3300	3300	3300	3300	3301	3300	3300	3299	3301	3298	3301	3301	3301	3301
22	3301	3301	3300	3300	3300	3301	3301	3301	3299	3301	3300	3301	3299	3299	3299
23	3302	3302	3304	3299	3300	3300	3300	3300	3299	3304	3302	3301	3300	3299	3299
25	3300	3300	3300	3301	3300	3300	3301	3300	3299	3304	3302	3301	3300	3300	3300
30	3299	3299	3301	3300	3300	3300	3301	3300	3301	3301	3299	3298	3300	3300	3300
40	3302	3302	3301	3299	3300	3301	3301	3300	3299	3301	3298	3300	3301	3301	3301

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	3299 bytes	–	100%
1,000	3299 bytes	–	100%
10,000	3299 bytes	–	100%
100,000	3298 bytes	-1 byte	26.96%
1,000,000	3298 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)	3310 bytes	+12 bytes (+0.36%)	–
1	3310 bytes	+12 bytes (+0.36%)	–
2	3330 bytes	+32 bytes (+0.97%)	+20 bytes
3	3331 bytes	+33 bytes (+1.00%)	+21 bytes
4	3362 bytes	+64 bytes (+1.94%)	+52 bytes
5	3389 bytes	+91 bytes (+2.76%)	+79 bytes
6	3422 bytes	+124 bytes (+3.76%)	+112 bytes
7	3459 bytes	+161 bytes (+4.88%)	+149 bytes
8	3494 bytes	+196 bytes (+5.94%)	+184 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	2967 bytes	-331 bytes (-10.04%)
Brotli (Wikipedia)	brotli	brotli -q 11	3061 bytes	-237 bytes (-7.19%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	3289 bytes	-9 bytes (-0.27%)
Zstandard (Wikipedia)	zstd	zstd -19	3327 bytes	+29 bytes (+0.88%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	3357 bytes	+59 bytes (+1.79%)
LZMA2 (Wikipedia)	xz	xz -9	3412 bytes	+114 bytes (+3.46%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3857 bytes	+559 bytes (+16.95%)

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.