Choose a version:
39% The original file has 216840 bytes (211.8k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 85260 bytes (83.3k, 39%).

After GZIP compression these minified files vary in size:
Microsoft
  37922 bytes (37.0k)
CDN, direct link
Boot
  34563 bytes (33.8k)
CDN, direct link
jsdelivr
  34563 bytes (33.8k)
CDN, direct link
Baidu
  29968 bytes (29.3k)
CDN, direct link
cdnjs
  29963 bytes (29.3k)
CDN, direct link
gzip -6 (default)
  29735 bytes (29.0k)
local copy
Google
  29715 bytes (29.0k)
CDN, direct link
cdnhttps
  29715 bytes (29.0k)
CDN, direct link
gzip -9
  29665 bytes (29.0k)
local copy
kzip -s0 -rn -b0
  28666 bytes (28.0k)
local copy
7zip -mx=9 -tgzip
  28656 bytes (28.0k)
local copy
libdeflate -12
  28605 bytes (27.9k)
local copy
Yandex
  28590 bytes (27.9k)
CDN, direct link
pigz -11 -n
  28572 bytes (27.9k)
local copy
Zopfli
  28556 bytes (27.9k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/jquery/jquery-1.5.1.min.js

You will automatically get the smallest jQuery 1.5.1 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 34 bytes by using my jQuery 1.5.1 Zopfli version instead of the best available CDN (0.12% smaller than Yandex, 28556 vs. 28590 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 --mls512 --bsr13 --lazy --ohh

(found October 21, 2015)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 512  --mls512
block splitting recursion 13  --bsr13
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 http://code.jquery.com/jquery-1.5.1.min.js --location | md5sum
b04a3bccd23ddeb7982143707a63ccf9  -
curl --silent --compressed http://minime.stephan-brumme.com/files/jquery/jquery-1.5.1.min.zopfli.js.gz | md5sum
b04a3bccd23ddeb7982143707a63ccf9  -

SHA1:
curl --silent --compressed http://code.jquery.com/jquery-1.5.1.min.js --location | sha1sum
4a5dc1389aad050a44ee5e81408238a317ab3413  -
curl --silent --compressed http://minime.stephan-brumme.com/files/jquery/jquery-1.5.1.min.zopfli.js.gz | sha1sum
4a5dc1389aad050a44ee5e81408238a317ab3413  -

These CDNs send you the original file:
CDN Size (compressed) MD5 (uncompressed) Timestamp
Microsoft 37922 bytes b04a3bccd23ddeb7982143707a63ccf9 (invalid)
Boot 34563 bytes b04a3bccd23ddeb7982143707a63ccf9 May 4, 2016 @ 09:17
jsdelivr 34563 bytes b04a3bccd23ddeb7982143707a63ccf9 (invalid)
cdnjs 29963 bytes b04a3bccd23ddeb7982143707a63ccf9 June 22, 2016 @ 22:04
Google 29715 bytes b04a3bccd23ddeb7982143707a63ccf9 (invalid)
cdnhttps 29715 bytes b04a3bccd23ddeb7982143707a63ccf9 November 24, 2016 @ 16:42
Yandex 28590 bytes b04a3bccd23ddeb7982143707a63ccf9 June 15, 2015 @ 21:17

And some CDNs send you a different file:
CDN Size (compressed) MD5 (uncompressed) Comment / Diff Timestamp
Baidu 29968 bytes c1b182682481636bf5bdde7ed6e8237d only whitespaces differ January 7, 2015 @ 10:16

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

Other Versions

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

3.2.1, 3.2.0,
3.1.1, 3.1.0,
3.0.0,
2.2.4, 2.2.3, 2.2.2, 2.2.1, 2.2.0,
2.1.4, 2.1.3, 2.1.2, 2.1.1, 2.1.0,
2.0.3, 2.0.2, 2.0.1, 2.0.0,
1.12.4, 1.12.3, 1.12.2, 1.12.1, 1.12.0,
1.11.3, 1.11.2, 1.11.1, 1.11.0,
1.10.2, 1.10.1, 1.10.0,
1.9.1, 1.9.0,
1.8.3, 1.8.2, 1.8.1, 1.8.0,
1.7.2, 1.7.1, 1.7.0,
1.6.4, 1.6.3, 1.6.2, 1.6.1, 1.6,
1.5.2, 1.5.1, 1.5,
1.4.4, 1.4.3, 1.4.2, 1.4.1, 1.4,
1.3.2, 1.3.1, 1.3,
1.2.6, 1.2.5, 1.2.4, 1.2.3, 1.2.2, 1.2.1, 1.2,
1.1.4, 1.1.3, 1.1.2, 1.1.1, 1.1,
1.0.4, 1.0.3, 1.0.2, 1.0.1, 1.0

The project site contains an overview how well these versions were compressed.
Other interesting projects are AngularJS, BackboneJS, Bootstrap, D3, Dojo, Ember, Knockout, lodash, React, Socket.IO, ThreeJS, UnderscoreJS and Vue.

Changelog

Best Zopfli parameters so far:
Size Improvement Parameters Found
28556 bytes -1 byte zopfli --i100000 --mls512 --bsr13 --lazy --ohh October 21, 2015 @ 12:05
28557 bytes -1 byte zopfli --i10000 --mls512 --bsr11 --lazy --ohh September 3, 2015 @ 09:30
28558 bytes -1 byte zopfli --i10000 --mls512 --bsr14 --lazy --ohh September 3, 2015 @ 09:14
28559 bytes -1 byte zopfli --i10000 --mls512 --bsr8 --lazy --ohh September 3, 2015 @ 09:13
28560 bytes -7 bytes zopfli --i10000 --mls512 --bsr6 --lazy --ohh September 1, 2015 @ 21:15
28567 bytes -3 bytes zopfli --i1000 --mls512 --bsr6 --lazy --ohh September 1, 2015 @ 20:38
28570 bytes zopfli --i100 --mls512 --bsr14 --lazy --ohh September 1, 2015 @ 20:20

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

Most recent activity on November 24, 2016 @ 16:42.

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
28576 28575 28575 28572 28572 28571 28578 28571 28571 28579 28569 28567 28569 28562 28574
28560 28563 28562 28562 28560 28559 28559 28562 28564 28568 28565 28561 28565 28565 28565
28560 28561 28570 28562 28560 28559 28562 28565 28560 28562 28565 28563 28560 28565 28562
28564 28561 28571 28558 28560 28567 28559 28565 28560 28561 28564 28567 28564 28564 28564
28560 28561 28568 28570 28560 28570 28561 28561 28559 28561 28563 28561 28563 28564 28561
28559 28562 28569 28559 28559 28559 28559 28559 28564 28567 28564 28567 28564 28564 28562
28560 28561 28568 28558 28558 28561 28559 28567 28560 28566 28564 28563 28566 28565 28561
28560 28560 28568 28564 28559 28558 28561 28562 28557 28559 28565 28566 28568 28565 28569
28565 28557 28571 28558 28558 28561 28561 28562 28559 28563 28561 28564 28562 28564 28564
28561 28561 28562 28559 28560 28560 28560 28566 28556 28562 28564 28564 28566 28564 28561
28560 28561 28569 28562 28558 28561 28561 28563 28557 28562 28563 28565 28561 28565 28566
28560 28559 28569 28558 28558 28561 28559 28562 28561 28563 28564 28564 28563 28564 28563
28563 28562 28559 28562 28560 28561 28559 28564 28560 28562 28562 28564 28561 28564 28562
28559 28558 28559 28562 28561 28561 28558 28564 28557 28561 28563 28564 28560 28565 28562
28560 28560 28568 28564 28558 28561 28559 28567 28562 28557 28562 28566 28563 28565 28563
28564 28560 28568 28562 28562 28567 28561 28560 28560 28560 28563 28564 28565 28564 28562
28559 28561 28570 28569 28558 28561 28559 28566 28560 28562 28563 28564 28564 28564 28563
28560 28559 28568 28567 28558 28562 28561 28567 28561 28563 28563 28563 28563 28565 28560
28560 28561 28570 28562 28561 28563 28560 28567 28558 28560 28563 28565 28563 28565 28566
28561 28560 28568 28558 28558 28562 28563 28567 28558 28561 28565 28564 28566 28564 28561
28560 28559 28569 28567 28560 28559 28560 28566 28560 28559 28561 28562 28564 28564 28562
28560 28560 28571 28558 28561 28561 28560 28565 28560 28562 28561 28563 28564 28564 28566
28565 28560 28568 28558 28558 28562 28560 28563 28559 28561 28564 28564 28564 28566 28563

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 28566 bytes 100%
1,000 28559 bytes -7 bytes 100%
10,000 28557 bytes -2 bytes 100%
100,000 28556 bytes -1 byte 2.03%
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
28666 bytes +110 bytes (+0.39%)
28666 bytes +110 bytes (+0.39%)
28711 bytes +155 bytes (+0.54%) +45 bytes
28699 bytes +143 bytes (+0.50%) +33 bytes
28705 bytes +149 bytes (+0.52%) +39 bytes
28742 bytes +186 bytes (+0.65%) +76 bytes
28765 bytes +209 bytes (+0.73%) +99 bytes
28786 bytes +230 bytes (+0.81%) +120 bytes
28815 bytes +259 bytes (+0.91%) +149 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
ZPAQ (Wikipedia) zpaq zpaq -method 69 23124 bytes -5432 bytes (-19.02%)
RAR (proprietary) RAR rar a -m5 -md64m -mc63:128t -mt1 23767 bytes -4789 bytes (-16.77%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 24958 bytes -3598 bytes (-12.60%)
Brotli (Wikipedia) brotli brotli -q 11 26386 bytes -2170 bytes (-7.60%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 26629 bytes -1927 bytes (-6.75%)
LZMA2 (Wikipedia) xz xz -9 27512 bytes -1044 bytes (-3.66%)
ZSTD (Wikipedia) zstd zstd -19 28096 bytes -460 bytes (-1.61%)

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