Currently best Zopfli settings

Save 2166 bytes by using my D3 3.3.5 Zopfli version instead of the best available CDN (4.54% smaller than unpkg, 47693 vs. 49859 bytes):
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 --mls2 --bsr12 --lazy --ohh

(found December 21, 2015)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	2	--mls2
block splitting recursion	12	--bsr12
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

Even Smaller Files Thanks To Defluff

Zopfli's output can be further optimized by the defluff tool.
In this particular case, defluff saves 2 more bytes (47691 bytes).

Verify file integrity

After decompression, my uncompressed files are identical to the original ones:

MD5:
curl --silent --compressed https://raw.githubusercontent.com/mbostock/d3/v3.3.5/d3.min.js --location | md5sum
d733da10a25e820e0bd90a3b397a948a  -
curl --silent --compressed https://minime.stephan-brumme.com/files/d3/d3-3.3.5.min.zopfli.js.gz | md5sum
d733da10a25e820e0bd90a3b397a948a  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/mbostock/d3/v3.3.5/d3.min.js --location | sha1sum
6ee01abea3702e369cba49956eef4fa47989b8c3  -
curl --silent --compressed https://minime.stephan-brumme.com/files/d3/d3-3.3.5.min.zopfli.js.gz | sha1sum
6ee01abea3702e369cba49956eef4fa47989b8c3  -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	57346 bytes	d733da10a25e820e0bd90a3b397a948a	(invalid)
cdnjs	50256 bytes	d733da10a25e820e0bd90a3b397a948a	(invalid)
unpkg	49859 bytes	d733da10a25e820e0bd90a3b397a948a	July 11, 2016 @ 16:31

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	50267 bytes	31cdf379ea7ce8c6c447fd2861157375	only whitespaces differ	(invalid)

Note: only the MD5 hashes are shown to keep things simple.

Other Versions

Available D3 versions at minime.stephan-brumme.com:

6.7.0, 6.6.2, 6.6.1, 6.6.0, 6.5.0, 6.4.0, 6.3.1, 6.2.0, 6.1.1, 6.1.0, 6.0.0,
5.16.0, 5.15.1, 5.15.0, 5.14.2, 5.14.1, 5.14.0, 5.13.1, 5.13.0, 5.12.0, 5.11.0, 5.10.1, 5.10.0,
5.9.7, 5.9.6, 5.9.5, 5.9.4, 5.9.3, 5.9.2, 5.9.1, 5.9.0, 5.8.2, 5.8.1, 5.8.0, 5.7.0, 5.6.0, 5.5.0, 5.4.0, 5.3.0, 5.2.0, 5.1.0, 5.0.1, 5.0.0,
4.13.0, 4.12.2, 4.12.1, 4.12.0, 4.11.0, 4.10.2, 4.10.1, 4.10.0,
4.9.1, 4.9.0, 4.8.0, 4.7.4, 4.7.3, 4.7.2, 4.7.1, 4.7.0, 4.6.0, 4.5.0, 4.4.4, 4.4.3, 4.4.2, 4.4.1, 4.4.0, 4.3.0, 4.2.8, 4.2.7, 4.2.6, 4.2.5, 4.2.4, 4.2.3, 4.2.2, 4.2.1, 4.2.0, 4.1.1, 4.1.0, 4.0.0,
3.5.17, 3.5.16, 3.5.15, 3.5.14, 3.5.13, 3.5.12, 3.5.11, 3.5.10, 3.5.9, 3.5.8, 3.5.7, 3.5.6, 3.5.5, 3.5.4, 3.5.3, 3.5.2, 3.5.1, 3.5.0, 3.4.13, 3.4.12, 3.4.11, 3.4.10, 3.4.9, 3.4.8, 3.4.6, 3.4.5, 3.4.4, 3.4.3, 3.4.2, 3.4.1, 3.4.0, 3.3.13, 3.3.12, 3.3.11, 3.3.10, 3.3.9, 3.3.8, 3.3.7, 3.3.6, 3.3.5, 3.3.4, 3.3.3, 3.3.2, 3.3.1, 3.3.0, 3.2.8, 3.2.7, 3.2.6, 3.2.5, 3.2.4, 3.2.3, 3.2.2, 3.2.1, 3.2.0, 3.1.10, 3.1.9, 3.1.8, 3.1.7, 3.1.6, 3.1.5, 3.1.4, 3.1.3, 3.1.2, 3.1.1, 3.1.0, 3.0.8, 3.0.7, 3.0.6, 3.0.5, 3.0.4, 3.0.3, 3.0.2, 3.0.1, 3.0.0

The project site contains an overview how well these versions were compressed.
Other interesting projects are AngularJS, BackboneJS, Bootstrap, Dojo, Ember, jQuery, Knockout, lodash, React, Socket.IO, ThreeJS, UnderscoreJS and Vue.

Changelog

Best Zopfli parameters so far:

Size	Improvement	Parameters	Found
47693 bytes	-8 bytes	zopfli --i100000 --mls2 --bsr12 --lazy --ohh	December 21, 2015 @ 18:44
47701 bytes	-2 bytes	zopfli --i10000 --mls2 --bsr12 --lazy --ohh	September 23, 2015 @ 19:49
47703 bytes	-21 bytes	zopfli --i1000 --mls2 --bsr12 --lazy --ohh	September 23, 2015 @ 07:54
47724 bytes	–	zopfli --i100 --mls2 --bsr12 --lazy --ohh	September 22, 2015 @ 11:22

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 or 100,000.

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	47812	47808	47855	47824	47827	47897	47891	47842	47869	47895	47895	47983	48005	47855	48001
4	47736	47796	47788	47784	47770	47761	47752	47804	47758	47758	47764	47746	47999	47790	48010
6	47734	47798	47785	47747	47798	47771	47795	47786	47784	47845	47767	47752	47976	47780	47877
7	47786	47824	47810	47796	47753	47748	47773	47743	47783	47781	47769	47753	47998	47833	47861
8	47737	47801	47822	47728	47771	47797	47808	47843	47771	47850	47848	47861	48004	47847	48009
9	47739	47825	47786	47754	47757	47794	47800	47793	47757	47751	47766	47745	47994	47856	48009
10	47783	47796	47786	47780	47803	47748	47829	47785	47804	47749	47764	47922	47998	47788	47859
11	47739	47814	47768	47745	47724	47789	47794	47781	47795	47852	47762	47751	47980	47740	47850
12	47693	47769	47767	47749	47796	47740	47787	47798	47799	47748	47759	47739	47998	47753	48007
13	47739	47799	47742	47745	47753	47763	47791	47805	47819	47752	47760	47754	47998	47753	47861
14	47752	47810	47773	47756	47747	47739	47791	47751	47821	47752	47762	47750	47998	47751	47860
15	47745	47802	47791	47780	47754	47794	47788	47848	47735	47753	47770	47743	47998	47734	47846
16	47747	47833	47766	47742	47743	47732	47791	47797	47795	47753	47743	47917	47998	47729	47852
17	47750	47816	47770	47744	47751	47749	47746	47745	47809	47751	47764	47752	47998	47758	47860
18	47776	47801	47818	47744	47756	47761	47802	47745	47782	47755	47761	47750	47998	47734	47870
19	47803	47814	47819	47744	47722	47787	47811	47813	47790	47755	47769	47742	47998	47749	47865
20	47738	47801	47768	47744	47743	47797	47790	47795	47754	47749	47767	47754	47979	48008	47869
21	47738	47794	47770	47748	47800	47764	47829	47772	47794	47754	47766	47757	47998	47761	47858
22	47749	47829	47767	47751	47751	47790	47801	47796	47781	47759	47764	47921	48000	47768	47861
23	47748	47788	47767	47745	47753	47791	47790	47797	47798	47750	47765	47756	47983	47738	47857
25	47793	47737	47789	47742	47763	47792	47776	47792	47795	47753	47760	47748	47998	47758	47852
30	47750	47778	47815	47747	47756	47793	47794	47798	47799	47752	47762	47753	47998	47760	47873
40	47759	47831	47755	47745	47756	47736	47789	47801	47789	47757	47765	47919	47998	47750	47863

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	47724 bytes	–	100%
1,000	47703 bytes	-21 bytes	100%
10,000	47701 bytes	-2 bytes	100%
100,000	47693 bytes	-8 bytes	0.29%
1,000,000	–	–	–
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)	48024 bytes	+331 bytes (+0.69%)	+201 bytes
1	48026 bytes	+333 bytes (+0.70%)	+203 bytes
2	48032 bytes	+339 bytes (+0.71%)	+209 bytes
3	47947 bytes	+254 bytes (+0.53%)	+124 bytes
4	47959 bytes	+266 bytes (+0.56%)	+136 bytes
5	47823 bytes	+130 bytes (+0.27%)	–
6	47845 bytes	+152 bytes (+0.32%)	+22 bytes
7	47831 bytes	+138 bytes (+0.29%)	+8 bytes
8	47835 bytes	+142 bytes (+0.30%)	+12 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
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	38257 bytes	-9436 bytes (-19.78%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	40479 bytes	-7214 bytes (-15.13%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	41197 bytes	-6496 bytes (-13.62%)
Brotli (Wikipedia)	brotli	brotli -q 11	43187 bytes	-4506 bytes (-9.45%)
LZMA2 (Wikipedia)	xz	xz -9	43912 bytes	-3781 bytes (-7.93%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	45689 bytes	-2004 bytes (-4.20%)
Zstandard (Wikipedia)	zstd	zstd -19	46215 bytes	-1478 bytes (-3.10%)

Detailled Analysis