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Convert GZ Archive Free

.gz: ten header bytes, a Deflate stream, eight trailer bytes

gzip wraps one Deflate stream in a header (optional name, time, OS) and a trailer (CRC-32 and length). Deflate itself is a run of blocks. Each block is stored, uses the fixed Huffman code or carries its own, and its tokens are either a literal byte or “copy N bytes from D back”. This page decodes every block with its own inflater, bit by bit, so you can see which words were copied and from where.

folder_openOpen .gz / .tgz / .svgzLog file sample.tar.gz with 3 membersdownloadDownload

access.log.gz: 220 log lines compressed by your browser’s Deflate, wrapped with name + time here

member 1 header, byte by byte21 header bytes · 8 trailer bytes

ID1 ID21F 8Bmagic 1F 8B

CM088 = Deflate (the only method defined)

FLG08FNAME

MTIME40 EE C0 6A2026-10-03T12:00:00Z (little-endian Unix time)

XFL000

OS033 = Unix

FNAME“access.log”original file name, Latin-1, NUL-terminated

CRC32D8 DC 8B 830x838BDCD8 = CRC-32 of the decompressed data ✓

ISIZEC8 79 00 0031,176 = original size mod 2³²

Members and Deflate blocks, to scale

width = compressed bits · click a block

gzip headerstored blockfixed Huffman blockdynamic Huffman blocktrailertrailing bytes

memberoffsetheaderstoredoriginalratioCRC-32ISIZE

10name “access.log” · 2026-10-03 12:00 · OS 32.4 KB31.2 KB7.7%matchmatch

#typeinout

1dynamic · last2.4 KB31.2 KB

Block 1: dynamic Huffmanbits 168-19,401 (byte 21, bit 0)

compressed2.4 KB (19,233 bits)

decompressed31.2 KB

bits per byte0.62

literals904

matches654

bytes from matches97.1%

longest match124 B

table header533 bits · HLIT 281 HDIST 30 HCLEN 14

first 900 tokens of 1,558 · highlighted text was copied from earlier output · hover for length and distance

203.0.113.7 - - [03/Oct/2026:09:00:02 +0000] "GET /favicon.ico HTTP/1.1" 500 6956 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:00:07 +0000] "GET /index.html HTTP/1.1" 200 26220 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:00:08 +0000] "GET /assets/app.css HTTP/1.1" 500 32172 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:00:17 +0000] "GET /assets/app.js HTTP/1.1" 200 13356 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:00:21 +0000] "GET / HTTP/1.1" 200 7204 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:00:27 +0000] "GET / HTTP/1.1" 200 22700 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:00:35 +0000] "GET /assets/app.css HTTP/1.1" 200 15660 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:00:41 +0000] "GET /api/orders?page=2 HTTP/1.1" 200 428 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:00:50 +0000] "GET /assets/app.js HTTP/1.1" 200 3372 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:00:51 +0000] "GET /favicon.ico HTTP/1.1" 200 30252 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:01:00 +0000] "GET /assets/app.js HTTP/1.1" 200 16492 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:01:06 +0000] "GET /index.html HTTP/1.1" 200 20012 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:01:13 +0000] "GET /api/orders?page=2 HTTP/1.1" 500 2412 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:01:16 +0000] "GET /images/logo.svg HTTP/1.1" 200 26796 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:01:22 +0000] "GET /assets/app.css HTTP/1.1" 200 33708 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:01:29 +0000] "GET / HTTP/1.1" 200 1580 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:01:35 +0000] "GET / HTTP/1.1" 200 38700 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:01:37 +0000] "GET /assets/app.js HTTP/1.1" 200 35500 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:01:46 +0000] "GET / HTTP/1.1" 200 47404 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:01:47 +0000] "GET /assets/app.js HTTP/1.1" 200 1196 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:01:51 +0000] "GET /images/logo.svg HTTP/1.1" 200 43308 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:01:58 +0000] "GET /favicon.ico HTTP/1.1" 200 48108 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:02:07 +0000] "GET / HTTP/1.1" 500 8044 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:02:13 +0000] "GET /api/orders?page=2 HTTP/1.1" 200 24620 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:02:15 +0000] "GET / HTTP/1.1" 200 9004 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:02:16 +0000] "GET /assets/app.css HTTP/1.1" 200 15660 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:02:18 +0000] "GET /api/orders?page=2 HTTP/1.1" 200 30636 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:02:22 +0000] "GET /index.html HTTP/1.1" 200 36268 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:02:26 +0000] "GET /images/logo.svg HTTP/1.1" 200 47404 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:02:30 +0000] "GET /images/logo.svg HTTP/1.1" 200 47404 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:02:32 +0000] "GET /assets/app.css HTTP/1.1" 200 6188 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:02:40 +0000] "GET /favicon.ico HTTP/1.1" 200 39596 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:02:48 +0000] "GET / HTTP/1.1" 200 10092 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:02:52 +0000] "GET /assets/app.js HTTP/1.1" 200 34732 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:02:57 +0000] "GET /images/logo.svg HTTP/1.1" 200 5676 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:02:59 +0000] "GET /assets/app.js HTTP/1.1" 200 41132 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:03:08 +0000] "GET /assets/app.css HTTP/1.1" 200 30700 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:03:16 +0000] "GET /favicon.ico HTTP/1.1" 500 24748 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:03:18 +0000] "GET /index.html HTTP/1.1" 200 9772 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:03:28 +0000] "GET /images/logo.svg HTTP/1.1" 200 5356 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:03:35 +0000] "GET /images/logo.svg HTTP/1.1" 200 12588 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:03:43 +0000] "GET /assets/app.css HTTP/1.1" 200 3756 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:03:47 +0000] "GET /api/orders?page=2 HTTP/1.1" 200 31916 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:03:56 +0000] "GET /favicon.ico HTTP/1.1" 200 14764 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:04:03 +0000] "GET /index.html HTTP/1.1" 200 13292 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:04:08 +0000] "GET /assets/app.js HTTP/1.1" 500 17452 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:04:18 +0000] "GET / HTTP/1.1" 200 6316 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:04:23 +0000] "GET /index.html HTTP/1.1" 200 2860 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:04:31 +0000] "GET / HTTP/1.1" 200 16940 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:04:33 +0000] "GET / HTTP/1.1" 200 19756 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:04:42 +0000] "GET /assets/app.js HTTP/1.1" 200 27820 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:04:46 +0000] "GET / HTTP/1.1" 200 28460 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:04:52 +0000] "GET /api/orders?page=2 HTTP/1.1" 500 35116 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:04:56 +0000] "GET /assets/app.css HTTP/1.1" 200 18604 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:04:57 +0000] "GET /api/orders?page=2 HTTP/1.1" 500 45740 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:05:04 +0000] "GET /assets/app.js HTTP/1.1" 500 13356 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:05:07 +0000] "GET /favicon.ico HTTP/1.1" 200 25708 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:05:16 +0000] "GET /api/orders?page=2 HTTP/1.1" 200 41836 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:05:18 +0000] "GET /assets/app.css HTTP/1.1" 500 13868 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:05:25 +0000] "GET /index.html HTTP/1.1" 200 36012 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:05:32 +0000] "GET /images/logo.svg HTTP/1.1" 200 43244 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:05:37 +0000] "GET /favicon.ico HTTP/1.1" 200 19820 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:05:39 +0000] "GET /assets/app.js HTTP/1.1" 200 22956 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:05:46 +0000] "GET /api/orders?page=2 HTTP/1.1" 200 43436 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:05:50 +0000] "GET / HTTP/1.1" 200 35244 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:05:55 +0000] "GET /api/orders?page=2 HTTP/1.1" 500 38572 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:06:00 +0000] "GET /images/logo.svg HTTP/1.1" 200 29036 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:06:05 +0000] "GET /assets/app.js HTTP/1.1" 200 34988 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:06:13 +0000] "GET / HTTP/1.1" 200 46124 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:06:21 +0000] "GET /assets/app.css HTTP/1.1" 200 20268 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:06:29 +0000] "GET /images/logo.svg HTTP/1.1" 200 22700 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:06:34 +0000] "GET /assets/app.js HTTP/1.1" 200 33196 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:06:39 +0000] "GET /api/orders?page=2 HTTP/1.1" 200 14828 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:06:43 +0000] "GET /assets/app.css HTTP/1.1" 500 32300 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:06:46 +0000] "GET /assets/app.css HTTP/1.1" 200 1196 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:06:52 +0000] "GET /api/orders?page=2 HTTP/1.1" 200 42412 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:06:58 +0000] "GET / HTTP/1.1" 500 10597 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:07:00 +0000] "GET /images/logo.svg HTTP/1.1" 200 44716 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:07:03 +0000] "GET /index.html HTTP/1.1" 200 26284 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:07:09 +0000] "GET /api/orders?page=2 HTTP/1.1" 200 28972 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:07:13 +0000] "GET / HTTP/1.1" 200 20652 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:07:18 +0000] "GET / HTTP/1.1" 500 34732 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:07:26 +0000] "GET /favicon.ico HTTP/1.1" 500 20268 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:07:34 +0000] "GET /favicon.ico HTTP/1.1" 200 300 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:07:40 +0000] "GET /api/orders?page=2 HTTP/1.1" 500 15660 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:07:47 +0000] "GET /assets/app.css HTTP/1.1" 200 20908 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:07:53 +0000] "GET / HTTP/1.1" 500 39212 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:07:57 +0000] "GET /index.html HTTP/1.1" 200 41964 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:07:59 +0000] "GET /images/logo.svg HTTP/1.1" 200 25708 "-" "curl/8.7.1"↵203.0.113.7 - - [03/Oct/2026:09:08:09 +0000] "GET /images/logo.svg HTTP/1.1" 200 7852 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"↵203.0.113.7 - - [03/Oct/2026:09:08:17 +0000] "GET /index.html HTTP/1.1" 200 39340 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"↵203.0.113.7 - - [03/Oct/2026:09:08:24 +0000] "GET /index.html HTTP/1.1" 200 91

literal bytecopy from close bycopy from far back

shortest literal codes in this block’s table

14 bit24 bit44 bit05 bit35 bit55 bit65 bit75 bit85 bit95 bit␠6 bit.6 bit:6 bit/7 bita7 bite7 bit

how many symbols get each code length

123456789101112131415

65 of 256 byte values appear; end-of-block takes 11 bits. Plain 8-bit bytes would be 249,408 bits; this block spends 19,233 including its own code table.

member 1 decompressed (31.2 KB)

nametypesizeowner · mtime

203.0.113.7 - - [03/Oct/2026:09:00:02 +0000] "GET /favicon.ico HTTP/1.1" 500 6956 "-" "curl/8.7.1"203.0.113.7 - - [03/Oct/2026:09:00:07 +0000] "GET /index.html HTTP/1.1" 200 26220 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"203.0.113.7 - - [03/Oct/2026:09:00:08 +0000] "GET /assets/app.css HTTP/1.1" 500 32172 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"203.0.113.7 - - [03/Oct/2026:09:00:17 +0000] "GET /assets/app.js HTTP/1.1" 200 13356 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"203.0.113.7 - - [03/Oct/2026:09:00:21 +0000] "GET / HTTP/1.1" 200 7204 "-" "curl/8.7.1"203.0.113.7 - - [03/Oct/2026:09:00:27 +0000] "GET / HTTP/1.1" 200 22700 "-" "curl/8.7.1"203.0.113.7 - - [03/Oct/2026:09:00:35 +0000] "GET /assets/app.css HTTP/1.1" 200 15660 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"203.0.113.7 - - [03/Oct/2026:09:00:41 +0000] "GET /api/orders?page=2 HTTP/1.1" 200 428 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"203.0.113.7 - - [03/Oct/2026:09:00:50 +0000] "GET /assets/app.js HTTP/1.1" 200 3372 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"203.0.113.7 - - [03/Oct/2026:09:00:51 +0000] "GET /favicon.ico HTTP/1.1" 200 30252 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Gecko/20100101 Firefox/131.0"203.0.113.7 - - [03/Oct/2026:09:01:00 +0000] "GET /assets/app.js HTTP/1.1" 200 16492 "-" "curl/8.7.1"203.0.113.7 - - [03/Oct/2026:09:01:06 +0000] "GET /index.html HTTP/1.1" 200 20012 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"203.0.113.7 - - [03/Oct/2026:09:01:13 +0000] "GET /api/orders?page=2 HTTP/1.1" 500 2412 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"203.0.113.7 - - [03/Oct/2026:09:01:16 +0000] "GET /images/logo.svg HTTP/1.1" 200 26796 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"203.0.113.7 - - [03/Oct/2026:09:01:22 +0000] "GET /assets/app.css HTTP/1.1" 200 33708 "-" "curl/8.7.1"203.0.113.7 - - [03/Oct/2026:09:01:29 +0000] "GET / HTTP/1.1" 200 1580 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"203.0.113.7 - - [03/Oct/2026:09:01:35 +0000] "GET / HTTP/1.1" 200 38700 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 14_6) AppleWebKit/605.1.15"203.0.113.7 - - [03/Oct/2026:09:01:37 +0000] "G…

check_circleCRC-32 and size check out.Decompressed 31.2 KB in 1 block(s); checksum 0x838BDCD8.

infoOriginal file name stored: “access.log”.gzip writes it unless you pass -n; it can leak local names, and gunzip -N restores it.

infoTimestamp stored.2026-10-03T12:00:00.000Z: two compressions of the same file differ by this alone.

check_circleBlock types used: dynamic Huffman.Encoders switch to stored when data won’t compress (random bytes, already-compressed files) and to the fixed code for tiny inputs where a custom table costs more than it saves.

wrapper & reproducibility lab · your browser’s own compressor

Same Deflate body, different files

The text is compressed once with CompressionStream, then wrapped as raw Deflate (as in ZIP and PNG), as zlib (as in PDF and HTTP “deflate”) and as gzip. gzip is written four ways: with a file name and the time, the same an hour later, and with no name and no time, which is what gzip -n writes. The compressed data never changes, but the hash does, which is why build tools that want byte-identical output pass -n.

input 180 B → Deflate body 113 B (62.8%) in dynamic block(s) · body sha256 69df488043a14822… in every row · your browser’s own gzip header: 1F 8B 08 00 00 00 00 00 00 0A (OS byte 10 = TOPS-20)

raw Deflateno header, no check (ZIP entries, PNG IDAT after zlib…)113 Bsha256 69df488043a14822…save

zlib78 9C + body + Adler-32 (PDF FlateDecode, HTTP “deflate”)119 Bsha256 ff52eaefe6fb12d2…save

gzip as the browser writes itCompressionStream("gzip") output, header as-is131 Bsha256 03827e1dbdf9d234…save

gzip, name + timeFNAME notes.txt, MTIME 12:00:00 UTC, OS Unix141 Bsha256 20020f68ece14544…save

gzip, an hour latersame name, MTIME 13:00:00141 Bsha256 de3c9d3da2b5f526…save

gzip -nno name, MTIME 0131 Bsha256 8f4bec69bf888024…save

gzip -n, againbuilt again from the same input131 Bsha256 8f4bec69bf888024… = identical to “gzip -n”save

Reference

bytesfieldmeaning (RFC 1952)

0-1ID1 ID21F 8B, always

2CM8 = Deflate; 0-7 reserved

3FLGbit 0 FTEXT, 1 FHCRC, 2 FEXTRA, 3 FNAME, 4 FCOMMENT, 5-7 must be 0

4-7MTIMEUnix time, little-endian; 0 = none

8XFL2 slowest/best, 4 fastest

9OSfilesystem the file came from (table at right)

+2+nFEXTRAXLEN, then subfields SI1 SI2 LEN data

…\0FNAMEoriginal name, ISO 8859-1, NUL-terminated

…\0FCOMMENTcomment, ISO 8859-1, NUL-terminated

+2FHCRClow 16 bits of the CRC-32 of the header

…DeflateRFC 1951 blocks: 3-bit header (BFINAL, BTYPE) each

−8CRC32 · ISIZECRC-32 of the original data, then its length mod 2³², both little-endian

OS byte

0FAT (MS-DOS, Windows)1Amiga2VMS3Unix4VM/CMS5Atari TOS6HPFS (OS/2)7Macintosh8Z-System9CP/M10TOPS-2011NTFS12QDOS13Acorn RISC OS255unknown

MIMEapplication/gzip (RFC 6713); older application/x-gzip

Extensions.gz; .tgz = .tar.gz; .svgz = gzipped SVG; .emz/.wmz gzipped metafiles

Magic bytes1F 8B 08 at offset 0

WindowDeflate copies reach at most 32,768 bytes back, lengths 3-258

Size limitnone on data, but ISIZE wraps at 4 GiB, so gzip -l shows the wrong size for bigger files

Ratio limitabout 1032:1 per Deflate stream (258-byte matches at roughly 2 bits each)

Relativeszlib (78 01/9C/DA) and raw Deflate share the body; BGZF and pigz output are valid gzip

Successorszstd and Brotli compress better and faster; HTTP uses gzip, br and zstd as Content-Encoding

1977LZ77Lempel and Ziv publish sliding-window compression.

1992gzip 0.1Jean-loup Gailly and Mark Adler release a patent-free replacement for Unix compress.

1993PKZIP 2 / DeflatePhil Katz’s Deflate becomes the shared algorithm of zip and gzip.

1995zlibThe library version, later used by PNG, HTTP, PDF and almost everything else.

1996RFC 1950-1952zlib, Deflate and gzip are published as informational RFCs.

1999HTTP/1.1Content-Encoding: gzip becomes standard on the web.

2013Zopfli · RFC 6713Google’s slow, denser Deflate encoder; application/gzip registered.

2016zstd 1.0Facebook’s successor; Brotli arrived in browsers the year before.

Where Deflate shows up next

Archive ConverterRepacks .tar.gz into ZIP, 7z or plain tar and checks every entry.release.tar.gzarrow_forwardrelease.zip · same files Archive toolsSafety inspector for archives: path traversal, symlinks, bombs and solid vs per-file reads.unknown.tgzarrow_forwardreport: 4 entries, no Zip Slip ZIP formatEvery ZIP entry is a raw Deflate body like the ones above, without the gzip header.file.gz · 18 B wrapperarrow_forwardfile in .zip · 30 B + name PDF CompressorPDF streams use the zlib wrapper: FlateDecode is Deflate with a 2-byte header.stream · FlateDecodearrow_forwardsmaller re-encoded stream SVG format.svgz is just SVG through gzip; browsers decode it when the server sends Content-Encoding.icon.svg · 12 KBarrow_forwardicon.svgz · 3 KB Hash GeneratorCheck a download against its published SHA-256, which only works if the .gz bytes are reproducible.pkg.tar.gzarrow_forwardsha256 match

sourcesRFC 1952 gzip RFC 1951 Deflate RFC 1950 zlib RFC 6713 media type GNU gzip manual Compression Streams