Choose a version:
53% The original file has 68890 bytes (67.3k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 36816 bytes (36.0k, 53%).

After GZIP compression these minified files vary in size:
Microsoft
  12929 bytes (12.6k)
CDN, direct link
Boot
  11779 bytes (11.5k)
CDN, direct link
MaxCDN
  11779 bytes (11.5k)
CDN, direct link
cdnjs
  9837 bytes (9.6k)
CDN, direct link
gzip -6 (default)
  9766 bytes (9.5k)
local copy
cdnhttps
  9743 bytes (9.5k)
CDN, direct link
fastcdn
  9741 bytes (9.5k)
CDN, direct link
gzip -9
  9741 bytes (9.5k)
local copy
unpkg
  9741 bytes (9.5k)
CDN, direct link
jsdelivr
  9722 bytes (9.5k)
CDN, direct link
libdeflate -12
  9441 bytes (9.2k)
local copy
7zip -mx=9 -tgzip
  9439 bytes (9.2k)
local copy
kzip -s0 -rn -b0
  9433 bytes (9.2k)
local copy
pigz -11 -n
  9383 bytes (9.2k)
local copy
Zopfli
  9373 bytes (9.2k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/bootstrap/bootstrap-3.3.5.min.js

You will automatically get the smallest Bootstrap 3.3.5 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 349 bytes by using my Bootstrap 3.3.5 Zopfli version instead of the best available CDN (3.72% smaller than jsdelivr, 9373 vs. 9722 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 --i10000000 --mb8 --mls64 --bsr30 --lazy --ohh

(found October 21, 2015)
Description Value Parameter
iterations 10000000  --i10000000
maximum blocks 8  --mb8
maximum length score 64  --mls64
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/twbs/bootstrap/v3.3.5/dist/js/bootstrap.min.js --location | md5sum
4becdc9104623e891fbb9d38bba01be4  -
curl --silent --compressed http://minime.stephan-brumme.com/files/bootstrap/bootstrap-3.3.5.min.zopfli.js.gz | md5sum
4becdc9104623e891fbb9d38bba01be4  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/twbs/bootstrap/v3.3.5/dist/js/bootstrap.min.js --location | sha1sum
6c264e0e0026ab5ece49350c6a8812398e696cbb  -
curl --silent --compressed http://minime.stephan-brumme.com/files/bootstrap/bootstrap-3.3.5.min.zopfli.js.gz | sha1sum
6c264e0e0026ab5ece49350c6a8812398e696cbb  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Microsoft 12929 bytes 4becdc9104623e891fbb9d38bba01be4 (invalid)
Boot 11779 bytes 4becdc9104623e891fbb9d38bba01be4 (invalid)
MaxCDN 11779 bytes 4becdc9104623e891fbb9d38bba01be4 (invalid)
cdnjs 9837 bytes 4becdc9104623e891fbb9d38bba01be4 (invalid)
cdnhttps 9743 bytes 4becdc9104623e891fbb9d38bba01be4 December 24, 2015 @ 07:36
fastcdn 9741 bytes 4becdc9104623e891fbb9d38bba01be4 November 6, 2015 @ 05:29
unpkg 9741 bytes 4becdc9104623e891fbb9d38bba01be4 July 11, 2016 @ 16:21
jsdelivr 9722 bytes 4becdc9104623e891fbb9d38bba01be4 (invalid)

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
9373 bytes -1 byte zopfli --i10000000 --mls64 --bsr30 --lazy --ohh October 21, 2015 @ 04:08
9374 bytes -1 byte zopfli --i100000 --mls512 --bsr6 --lazy --ohh September 10, 2015 @ 21:02
9375 bytes -1 byte zopfli --i10000 --mls1024 --bsr11 --lazy --ohh September 10, 2015 @ 16:59
9376 bytes -1 byte zopfli --i1000 --mls512 --bsr4 --lazy --ohh September 10, 2015 @ 16:32
9377 bytes zopfli --i100 --mls1024 --bsr11 --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:
100,000 or 10,000,000.
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
9384 9384 9385 9384 9384 9384 9385 9387 9391 9392 9380 9379 9388 9385 9385
9378 9378 9375 9376 9375 9375 9375 9375 9375 9375 9375 9385 9384 9378 9378
9377 9377 9376 9376 9376 9375 9375 9375 9374 9376 9377 9376 9378 9378 9375
9375 9375 9376 9376 9376 9375 9376 9375 9375 9375 9378 9379 9379 9378 9379
9375 9375 9376 9375 9375 9375 9376 9375 9375 9375 9378 9378 9380 9378 9378
9377 9377 9377 9376 9378 9378 9376 9375 9375 9375 9378 9375 9377 9377 9378
9375 9375 9376 9375 9376 9379 9376 9375 9375 9375 9379 9378 9378 9379 9378
9375 9375 9375 9376 9376 9375 9380 9375 9375 9375 9378 9379 9380 9378 9375
9375 9375 9375 9376 9375 9375 9375 9375 9375 9375 9375 9378 9379 9377 9375
9375 9375 9376 9378 9376 9375 9375 9375 9374 9375 9378 9375 9377 9378 9375
9375 9375 9375 9376 9375 9375 9376 9375 9375 9375 9378 9378 9377 9378 9377
9375 9375 9375 9375 9376 9375 9375 9375 9375 9375 9378 9383 9380 9377 9377
9375 9375 9375 9376 9375 9375 9375 9375 9376 9375 9378 9377 9378 9378 9378
9375 9375 9375 9375 9376 9375 9375 9375 9375 9375 9378 9375 9377 9378 9378
9375 9375 9375 9376 9376 9375 9376 9375 9375 9375 9378 9378 9378 9378 9378
9375 9375 9375 9376 9375 9375 9376 9375 9374 9375 9378 9383 9379 9378 9378
9375 9375 9376 9376 9376 9375 9376 9375 9375 9375 9374 9378 9378 9378 9378
9375 9375 9375 9375 9375 9375 9376 9375 9375 9375 9379 9375 9377 9378 9375
9375 9375 9376 9375 9376 9375 9376 9375 9375 9375 9378 9375 9377 9378 9378
9375 9375 9376 9376 9375 9375 9376 9375 9375 9375 9378 9379 9380 9378 9378
9375 9375 9375 9375 9375 9375 9376 9375 9375 9375 9378 9377 9379 9378 9378
9376 9376 9375 9375 9375 9373 9375 9375 9375 9375 9379 9375 9377 9378 9378
9375 9375 9375 9376 9375 9376 9375 9375 9375 9375 9375 9377 9379 9377 9378

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 9377 bytes 100%
1,000 9375 bytes -2 bytes 100%
10,000 9375 bytes 100%
100,000 9374 bytes -1 byte 100%
1,000,000 9374 bytes 1.45%
10,000,000 9373 bytes -1 byte 1.45%

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
9433 bytes +60 bytes (+0.64%)
9433 bytes +60 bytes (+0.64%)
9436 bytes +63 bytes (+0.67%) +3 bytes
9459 bytes +86 bytes (+0.92%) +26 bytes
9468 bytes +95 bytes (+1.01%) +35 bytes
9511 bytes +138 bytes (+1.47%) +78 bytes
9554 bytes +181 bytes (+1.93%) +121 bytes
9584 bytes +211 bytes (+2.25%) +151 bytes
9630 bytes +257 bytes (+2.74%) +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 7805 bytes -1568 bytes (-16.73%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 8477 bytes -896 bytes (-9.56%)
Brotli (Wikipedia) brotli brotli -q 11 8637 bytes -736 bytes (-7.85%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 8858 bytes -515 bytes (-5.49%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 9100 bytes -273 bytes (-2.91%)
LZMA2 (Wikipedia) xz xz -9 9328 bytes -45 bytes (-0.48%)
ZSTD (Wikipedia) zstd zstd -19 9388 bytes +15 bytes (+0.16%)

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