Choose a version:
53% The original file has 67546 bytes (66.0k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 35951 bytes (35.1k, 53%).

After GZIP compression these minified files vary in size:
Microsoft
  12554 bytes (12.3k)
CDN, direct link
Boot
  11490 bytes (11.2k)
CDN, direct link
MaxCDN
  11489 bytes (11.2k)
CDN, direct link
unpkg
  11149 bytes (10.9k)
CDN, direct link
Baidu
  9619 bytes (9.4k)
CDN, direct link
cdnjs
  9619 bytes (9.4k)
CDN, direct link
gzip -6 (default)
  9561 bytes (9.3k)
local copy
cdnhttps
  9538 bytes (9.3k)
CDN, direct link
gzip -9
  9535 bytes (9.3k)
local copy
Yandex
  9517 bytes (9.3k)
CDN, direct link
jsdelivr
  9517 bytes (9.3k)
CDN, direct link
7zip -mx=9 -tgzip
  9232 bytes (9.0k)
local copy
libdeflate -12
  9232 bytes (9.0k)
local copy
kzip -s0 -rn -b1
  9228 bytes (9.0k)
local copy
pigz -11 -n
  9174 bytes (9.0k)
local copy
Zopfli
  9163 bytes (8.9k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/bootstrap/bootstrap-3.3.4.min.js

You will automatically get the smallest Bootstrap 3.3.4 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 354 bytes by using my Bootstrap 3.3.4 Zopfli version instead of the best available CDN (3.86% smaller than jsdelivr, 9163 vs. 9517 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 --i10000 --mb8 --mls128 --bsr7 --lazy --ohh

(found September 11, 2015)
Description Value Parameter
iterations 10000  --i10000
maximum blocks 8  --mb8
maximum length score 128  --mls128
block splitting recursion 7  --bsr7
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/twbs/bootstrap/v3.3.4/dist/js/bootstrap.min.js --location | md5sum
8c237312864d2e4c4f03544cd4f9b195  -
curl --silent --compressed http://minime.stephan-brumme.com/files/bootstrap/bootstrap-3.3.4.min.zopfli.js.gz | md5sum
8c237312864d2e4c4f03544cd4f9b195  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/twbs/bootstrap/v3.3.4/dist/js/bootstrap.min.js --location | sha1sum
253711c6d825de55a8360552573be950da180614  -
curl --silent --compressed http://minime.stephan-brumme.com/files/bootstrap/bootstrap-3.3.4.min.zopfli.js.gz | sha1sum
253711c6d825de55a8360552573be950da180614  -

These CDNs send you the original file:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Microsoft 12554 bytes 8c237312864d2e4c4f03544cd4f9b195 (invalid)
MaxCDN 11489 bytes 8c237312864d2e4c4f03544cd4f9b195 (invalid)
Baidu 9619 bytes 8c237312864d2e4c4f03544cd4f9b195 (invalid)
Yandex 9517 bytes 8c237312864d2e4c4f03544cd4f9b195 (invalid)
jsdelivr 9517 bytes 8c237312864d2e4c4f03544cd4f9b195 (invalid)

And some CDNs send you a different file:
CDN Size (compressed) MD5 (uncompressed) Comment / Diff Timestamp
Boot 11490 bytes b6d6c550cb657155feb06fdcd34b73cb < if("undefined"==typeof jQuery)throw new Error("Bootstrap's [...]
< var e=c.find(".active:last a"),f=a.Event("hide.bs.tab",{re [...]
> if("undefined"==typeof jQuery)throw new Error("Bootstrap's [...]
> if(e.trigger(f),b.trigger(g),!g.isDefaultPrevented()&&!f.i [...]
(invalid)
unpkg 11149 bytes b6d6c550cb657155feb06fdcd34b73cb < if("undefined"==typeof jQuery)throw new Error("Bootstrap's [...]
< var e=c.find(".active:last a"),f=a.Event("hide.bs.tab",{re [...]
> if("undefined"==typeof jQuery)throw new Error("Bootstrap's [...]
> if(e.trigger(f),b.trigger(g),!g.isDefaultPrevented()&&!f.i [...]
July 11, 2016 @ 16:21
cdnjs 9619 bytes b6d6c550cb657155feb06fdcd34b73cb < if("undefined"==typeof jQuery)throw new Error("Bootstrap's [...]
< var e=c.find(".active:last a"),f=a.Event("hide.bs.tab",{re [...]
> if("undefined"==typeof jQuery)throw new Error("Bootstrap's [...]
> if(e.trigger(f),b.trigger(g),!g.isDefaultPrevented()&&!f.i [...]
(invalid)
cdnhttps 9538 bytes b6d6c550cb657155feb06fdcd34b73cb < if("undefined"==typeof jQuery)throw new Error("Bootstrap's [...]
< var e=c.find(".active:last a"),f=a.Event("hide.bs.tab",{re [...]
> if("undefined"==typeof jQuery)throw new Error("Bootstrap's [...]
> if(e.trigger(f),b.trigger(g),!g.isDefaultPrevented()&&!f.i [...]
December 24, 2015 @ 07:36

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

Other Versions

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

3.3.7, 3.3.6, 3.3.5, 3.3.4, 3.3.2, 3.3.1, 3.3.0,
3.2.0,
3.1.1, 3.1.0,
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, D3, Dojo, Ember, jQuery, Knockout, lodash, React, Socket.IO, ThreeJS, UnderscoreJS and Vue.

Changelog

Best Zopfli parameters so far:
Size Improvement Parameters Found
9163 bytes -1 byte zopfli --i10000 --mls128 --bsr7 --lazy --ohh September 11, 2015 @ 14:41
9164 bytes -1 byte zopfli --i10000 --mls2048 --bsr11 --lazy --ohh September 10, 2015 @ 17:15
9165 bytes -1 byte zopfli --i1000 --mls1024 --bsr8 --lazy --ohh September 10, 2015 @ 16:34
9166 bytes -1 byte zopfli --i1000 --mls512 --bsr13 --lazy --ohh September 10, 2015 @ 16:33
9167 bytes zopfli --i100 --mls512 --bsr4 --lazy --ohh September 10, 2015 @ 16:27

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

Most recent activity on July 11, 2016 @ 16:21.

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
9178 9178 9178 9178 9166 9177 9176 9178 9177 9180 9182 9180 9177 9166 9177
9165 9165 9166 9165 9165 9166 9166 9169 9165 9164 9165 9169 9168 9169 9165
9165 9165 9165 9165 9165 9165 9169 9170 9164 9166 9165 9169 9165 9165 9163
9166 9166 9166 9165 9165 9165 9163 9171 9169 9171 9163 9169 9168 9166 9166
9163 9163 9163 9164 9166 9165 9166 9168 9164 9164 9167 9169 9165 9168 9165
9165 9165 9165 9166 9165 9165 9169 9169 9165 9169 9164 9168 9168 9169 9163
9165 9165 9166 9165 9166 9165 9166 9171 9168 9168 9165 9167 9170 9169 9166
9165 9165 9166 9165 9165 9165 9165 9165 9164 9168 9164 9169 9165 9166 9166
9165 9165 9166 9165 9165 9165 9166 9168 9164 9169 9164 9169 9169 9167 9165
9165 9165 9166 9165 9165 9165 9166 9168 9164 9168 9164 9169 9168 9166 9166
9165 9165 9164 9166 9165 9165 9166 9170 9164 9170 9165 9169 9169 9166 9166
9165 9165 9165 9165 9165 9165 9166 9168 9170 9169 9164 9176 9168 9165 9163
9165 9165 9165 9165 9165 9165 9165 9166 9164 9166 9169 9167 9165 9163 9164
9165 9165 9165 9166 9165 9165 9165 9168 9170 9165 9163 9167 9165 9165 9165
9166 9166 9166 9165 9165 9165 9165 9168 9165 9169 9164 9168 9168 9167 9166
9165 9165 9166 9165 9165 9165 9165 9165 9169 9169 9165 9168 9169 9165 9166
9165 9165 9165 9166 9165 9165 9165 9165 9165 9168 9165 9176 9165 9165 9166
9165 9165 9165 9165 9166 9165 9163 9168 9165 9168 9165 9167 9168 9165 9166
9165 9165 9165 9163 9166 9165 9163 9165 9165 9169 9164 9169 9170 9166 9165
9165 9165 9166 9166 9165 9165 9167 9165 9165 9168 9163 9168 9168 9165 9165
9165 9165 9166 9165 9165 9165 9165 9165 9165 9165 9164 9169 9168 9166 9166
9165 9165 9165 9164 9165 9165 9167 9169 9165 9170 9165 9167 9168 9166 9165
9165 9165 9166 9166 9165 9166 9165 9168 9165 9168 9166 9168 9165 9165 9165

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 9166 bytes 100%
1,000 9164 bytes -2 bytes 100%
10,000 9163 bytes -1 byte 100%
100,000 9163 bytes 13.91%
1,000,000 9163 bytes 4.06%
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
9229 bytes +66 bytes (+0.72%) +1 byte
9228 bytes +65 bytes (+0.71%)
9231 bytes +68 bytes (+0.74%) +3 bytes
9254 bytes +91 bytes (+0.99%) +26 bytes
9261 bytes +98 bytes (+1.07%) +33 bytes
9305 bytes +142 bytes (+1.55%) +77 bytes
9348 bytes +185 bytes (+2.02%) +120 bytes
9380 bytes +217 bytes (+2.37%) +152 bytes
9425 bytes +262 bytes (+2.86%) +197 bytes

Non-DEFLATE Algorithms

Archivers based on completely different compression algorithms often produce superior results.
Unfortunately, browsers only support gzip compression at the moment.
Algorithm Program Parameters Size Compared To Best Zopfli
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 7647 bytes -1516 bytes (-16.54%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 8328 bytes -835 bytes (-9.11%)
Brotli (Wikipedia) brotli brotli -q 11 8445 bytes -718 bytes (-7.84%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 8695 bytes -468 bytes (-5.11%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 8928 bytes -235 bytes (-2.56%)
LZMA2 (Wikipedia) xz xz -9 9116 bytes -47 bytes (-0.51%)
ZSTD (Wikipedia) zstd zstd -19 9184 bytes +21 bytes (+0.23%)

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):


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 2017.
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