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TLDs that are also file extensions

There has recently been some concerns expressed around new TLDs colliding with file extensions. While I’m the first to raise concerns around collisions, I think that this particular ship has sailed. As an example, the DEC VAX and CP/M used .COM as a file extension. This was then carried over into MS-DOS (and Windows) - a good example of this being While this confusion was briefly abused, but mitigations were quickly put in place. This is a great example of the contextual important of naming - on your computer is a different context to - the 3M Command Adhesive website.

However, before completely dismissing the threat, I figured I’d quickly look and see how many collisions there are between well known file extensions and delegated TLDs. I used the Webopedia List Of Data Formats & File Extensions and wrote a small Python program to compare these with the IANA list of delegated TLDs

Here are the results:

Extension Description
abc ActionScript Byte Code File
ad Screen saver data (AfterDark)
ads Ada Package Specification
afl Font file (for Allways) (Lotus 1-2-3)
ag Applixware graphics file
ai Vector graphics (Adobe Illustrator)
app Add-in application file (Symphony)
art Graphics (scrapbook) (Art Import)
au Sound (audio) file (SUN Microsystems)
aw Text file (HP AdvanceWrite)
ax DirectShow Filter
bar Horizontal bar menu object file (dBASE Application Generator)
bb Database backup (Papyrus)
bcn Business Card Pro Design
bid BidMaker 2002 file
bio OS/2 BIOS
bm Bitmap graphics
bom MicroSim PCBoard Bill of Materials
boo Compressed file ASCII archive created by BOO (msbooasm.arc)
book Adobe FrameMaker Book
bot Linkbot file
box Myriad Jukebox file
br Script (Bridge)
buy Datafile format (movie)
ca Initial cache data for root domain servers (Telnet)
cab Cabinet File (Microsoft installation archive)
cal Calendar file (Windows 3.x)
cam Casio Camera Graphic
car AtHome Assistant file
cat Catalog (dBASE IV)
cc C++ source code file
cf Sendmail Configuration file
ch Header file (Clipper 5)
cl Common LISP source code file
cm Data file (CraftMan)
com Command (memory image of executable program) (DOS)
crs File Conversion Resource (WordPerfect 5.1)
data Sid Tune audio file
day Journal file
de MetaProducts Download Express incompletely downloaded file
dev Device driver
do ModelSim Filter Design HDL Coder
dog Screen file (Laughing Dog Screen Maker)
dot Line-type definition file (CorelDRAW)
dvr Windows Media Center Recorded file
dz Dzip Compressed file
eco NetManage ECCO file
email Outlook Express Mail Message
fi Interface file (MS Fortran)
fit Fits graphics
fm Spreatsheet (FileMaker Pro)
frl FormFlow file
gal Corel Multimedia Manager Album
gb Pagefox Bitmap Image file
gg Google Desktop Gadget file
gl Animation (GRASP GRAphical System for Presentation)
gp Geode parameter file (Geoworks Glue)
ibm Compressed file archive created by ARCHDOS (Internal IBM only)
id Disk identification file
inc Include file (several programming languages)
ink Pantone reference fills file (CorelDRAW)
int Borland Interface Units
io Compressed file archive created by CPIO
ist Digitrakker Instrument File (n-FaCToR)
it Settings (intalk)
java Java source code file
lat Crossword Express Lattice file
man Command manual
map Color palette
md Compressed file archive created by MDCD (mdcd10.arc)
me Usually ASCII text file READ.ME
med Macro Editor delete save (WordPerfect Library)
mk Makefile
mlb Macro library file (Symphony)
mm Text file (MultiMate Advantage II)
mov QuickTime Video Clip
msd MS Diagnostic Utility Report
mu Menu (Quattro Pro)
nc Graphics (netcdf)
net Network configuration/info file
new New info
ng Online documentation database (Norton Guide)
now Text file
np Project schedule (Nokia Planner) (Visual Planner 3.x)
nra Nero Audio-CD Compilation
nrw Nero WMA Compilation file
one OneNote Document File
org Calendar file (Lotus Organizer)
pa Print Artist
pet Program Editor top overflow file (WordPerfect Library)
pf Windows Prefetch file
pg Pagefox File
ph Optimized .goh file (Geoworks)
pk Packed bitmap font bitmap file (TeX DVI drivers)
pl Perl source code file
pro Prolog source code file
ps PostScript file (text/graphics) (ASCII)
pub Page template (MS Publisher)
pw Text file (Professional Write)
py Python script file
red Path info (Clarion Modula-2)
rip Graphics (Remote Access)
rs Data file (Amiga Resource – Reassembler)
ru JavaSoft Library file
run RunScanner Saved file
sas SAS System program
sb Audio file (signed byte)
sbi Sound Blaster Instrument file (Creative Labs)
sbs SWAT HRU Output file
sc Pal script (Paradox)
sca Datafile (SCA)
sh Unix shell script
skin Skin file
sl S-Lang source code file
sm Smalltalk source code file
so Apache Module file
spa Macromedia FutureSplash file
ss Bitmap graphics (Splash)
st Smalltalk source code file (Little Smalltalk)
tab Guitar Tablature file
tax TurboTax file
tc Configuration (Turbo C – Borland C++)
td Configuration file (Turbo Debugger for DOS)
tdk Keystroke recording file (Turbo Debugger)
tel Host file (Telnet)
tf Configuration (Turbo Profiler)
thd Thread
tr Session-state settings (Turbo Debugger for DOS)
tv Table view settings (Paradox)
tz Compressed file archive created by TAR and COMPRESS (.tar.Z)
vc Include file with color definitions (Vivid 2.0)
vi Graphics (Jovian Logic VI)
win Opera Saved Window file
wow Music (8 channels) (Grave Mod Player)
ws Text file (WordStar 5.0-6.0)
xxx Singer Sewing Machine Professional SewWare file
xyz ASCII RPG Maker Graphic Format
zip ZIP Compressed file archive

Total: 139

Quick-n-dirty Python to generate this:

#!/usr/bin/env python3

PoC to find file extensions that are also valid TLDs
import sys

def read_filelist(filename):
  file_types = {}
  with open(filename) as f:
    lines = f.readlines()
    for line in lines:
      if line.startswith('.'):
        (ext, desc) = line.split(' ', 1)
        ext = ext.strip('.')
        file_types[ext] = desc.strip()
  return file_types

def read_tlds(filename):
  tlds = []
  with open(filename) as f:
    lines = f.readlines()
    for line in lines:
  return tlds

def main():
  """pylint FTW"""
  tlds = read_tlds('tlds-alpha-by-domain.txt')
  extensions = read_filelist('file_extension_tlds.txt')
  print ("| Extension | Description |")
  print ("| --------- | ----------- |")
  for ext in extensions:
    if ext in tlds:
      print ("| %s | %s |" % (ext, extensions[ext]))

if __name__ == "__main__":