File associations

Tell Windows that a given file extension opens with your app (e.g., .MyApp opens in My Application).

Applies to: MSI and MSIX.

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fileAssociations – open-with handlers

Properties

Property	Type	Required	Default	Description
fileType	string	yes	–	File extension without the leading dot, e.g., "MyApp".
executable	string	yes	–	The exe that opens the file. Usually $.installDir\\….
icon	string	no	–	Source .ico/.png/.exe/.dll for the document icon. Append ,index for exe/dll.
progId	string	no	<fileType>_auto_file	The Programmatic ID. Override with a brand prefix (e.g., "MyApp.Document.1") to avoid collisions when multiple installers register the same extension.
verbs	array of Verb	no	[ { "name": "Open", "arguments": "\"%1\"" } ]	Verbs the user can invoke ("Open", "Edit", "Print", …).

Verb

Property	Type	Required	Default	Description
name	string	yes	–	The verb name shown in Explorer ("Open", "Edit", "Print", …).
arguments	string	no	–	Arguments passed to executable for this verb. %1 is the selected file.

Examples

Single-extension association

"fileAssociations": [
  {
    "fileType":   "My Company",
    "executable": "$.installDir\\MyApp.exe",
    "icon":       "installer-assets\\My Company-doc.ico"
  }
]

Default verb is Open with "%1".

Multiple verbs (Open, Edit, Print)

"fileAssociations": [
  {
    "fileType":   "My Company",
    "executable": "$.installDir\\MyApp.exe",
    "icon":       "installer-assets\\My Company-doc.ico",
    "verbs": [
      { "name": "Open",  "arguments": "\"%1\"" },
      { "name": "Edit",  "arguments": "--edit \"%1\"" },
      { "name": "Print", "arguments": "--print \"%1\"" }
    ]
  }
]

Multiple extensions handled the same way

fileAssociations is an array, so repeat the entry per extension:

"fileAssociations": [
  { "fileType": "My Company",    "executable": "$.installDir\\MyApp.exe" },
  { "fileType": "My Companynote","executable": "$.installDir\\MyApp.exe" }
]

If you want the same ProgID across extensions, set progId explicitly on each entry.

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MSI vs MSIX behavior

Aspect	MSI	MSIX
fileAssociations	Implemented via Win32 file association registry entries.	Declared in the MSIX manifest under Extensions.
Multiple verbs	Supported.	Supported (Open verb is mandatory for the package).

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Validation rules

Validator	Catch
required	fileType, executable are mandatory.
valid path	executable must be a syntactically valid path.
valid icon source	icon must be .ico/.png/.exe/.dll.

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