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Version: 2.0.1

Build Status

Python script to add file extensions to files without them, based on Siegfried format identification.

Calling addext takes two positional arguments:

  • target: Path to target file or directory
  • json: Path to addext PRONOM JSON file (pronom_v95.json is included in this repository for convenience. See PRONOM JSON file section below for instructions on how to create a new JSON file in expected format from PRONOM XML exports)

Options include:

  • -d, --dryrun: Perform dry run (print would-be changes to terminal instead of renaming files)
  • -m, --manual: Manually choose extension to add to files when PRONOM gives several options (not available in Windows)


Default mode

In its default mode, addext adds file extensions to files if they meet a few conditions:

  • Siegfried can positively identify a PUID for the file
  • There is at least one file extension associated with the PUID in PRONOM
  • The file does not already have one of the extensions listed in PRONOM for that PUID (case-insensitive)

If all conditions are met, addext adds the file extension to the file in-place. It is recommended that you try a dry run first to evaluate the proposed changes before renaming files.

Manual mode

In -m, --manual mode, addext follows the following logic:

  • If Siegfried cannot positively identify a PUID for the file, skip the file
  • If there is only one file extension associated with the PUID in PRONOM and the file does not already have this extension (case-insensitive), add the extension
  • If there is more than one file extension associated with the PUID in PRONOM and the file does not already have this extension, allow the user to choose which extension to add and then modify the filename in-place

Note that for directories with many files, going through the files one-by-one in manual mode may take some time. Running addext as a dry run in manual mode may help give an idea of the extent of manual choices you will be asked to make.

Due to its dependency on Inquirer, manual mode is not available on Windows.


  • Python 3.6+
  • Siegfried
  • Inquirer: For selection between extension options in -m, --manual mode (Linux/macOS only); installed with pip install inquirer


Install Siegfried

Install Siegfried following the instructions found here.

Install via git clone/download

The easiest way to use addext is to clone or download this repository and then run the script with python3 /path/to/ [options].

If taking this route, install additional Python library dependencies: pip install -r requirements.txt or pip install inquirer (this may require sudo permissions).

Install via PyPI

addext can also be installed via pip install addext. This will install a script in the /usr/local/bin directory (assuming a Linux/macOS installation) so that addext can be called from anywhere with simply [options].

Note that following installation, you will need to download or create a PRONOM JSON file to use with addext.



The PRONOM JSON file is a lightweight representation of information from PRONOM needed for addext to function. The file contains an object for each format described with a PRONOM ID (PUID), structured like the following example:

"fmt/858": {
    "file_format": "Navisworks Document",
    "version": "2010",
    "file_extensions": [

Updating the PRONOM JSON file

pronom_v95.json is currently up-to-date with PRONOM release v95.

To create a new PRONOM JSON file (for instance, after a new PRONOM release):

  • Get PRONOM XML export from Ross Spencer's Release repository for The Skeleton Test Suite, which provides a set of DOIs for archives of PRONOM releases.
  • Run addext/ to create a new PRONOM JSON file from the XML exports: python3 /path/to/pronom/export/directory pronom.json


  • Canadian Centre for Architecture
  • Tessa Walsh

This project was initially developed in 2016-2017 for the Canadian Centre for Architecture by Tessa Walsh, Digital Archivist, as part of the development of the Archaeology of the Digital project.


Python script to add file extensions based on PRONOM ID (PUID)








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