Say I use a predefined serialization format X for certain data. Should I indicate the application in a custom filename extension or not? It is quite common

  • pk3 is a zip archive
  • XSL, SVG and many others are XML files
  • Some files are INI files

It is practical to denote the purpose of the file, but

  • I am unhappy to invent another filename extension (there are already too many)
  • It hides the fact that the user can use any program that can read and write X can be used to manipulate data (obfuscation)

I am interested in what is recommended in the following scenarios:

  1. Program configuration data
  2. Input files for code generation scripts
  3. Saved program state
  4. Plug-in bundle zip archive
  • Can you tell us more about your specific use case? There are pros & cons to both approaches and no one can really say without having some details.
    – RubberDuck
    Oct 7, 2016 at 8:24
  • 2
    Invent a new one and don't restrict yourself to three characters. Oct 7, 2016 at 8:47
  • @CodesInChaos Would you say, there is no upper limit
    – user877329
    Oct 7, 2016 at 8:50
  • 2
    @user877329 Most of mine are 10-20 characters. That's usually enough for a meaningful unique name (e.g. .FirefoxPlugin, .MsExcelSheet) Oct 7, 2016 at 9:07
  • What do you want to happen when a Windows user double clicks on your file? A custom file extension in that case makes it easy to launch your application.
    – Brandin
    Oct 7, 2016 at 10:14


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