FIDO logo

Open source Format Identification of Digital Objects

Currently v1.3.4

Usage [-h] [-v] [-q] [-recurse] [-zip] [-nocontainer] [-pronom_only]
         [-input INPUT] [-filename FILENAME] [-useformats INCLUDEPUIDS]
         [-nouseformats EXCLUDEPUIDS] [-matchprintf FORMATSTRING]
         [-nomatchprintf FORMATSTRING] [-bufsize BUFSIZE]
         [-container_bufsize CONTAINER_BUFSIZE]
         [-loadformats XML1,...,XMLn] [-confdir CONFDIR]
         [FILE [FILE ...]]

  Format Identification for Digital Objects (fido).
  FIDO is a command-line tool to identify the file formats of digital objects.
  It is designed for simple integration into automated work-flows.

positional arguments:
  FILE                  files to check. If the file is -, then read content from stdin. In this case, python must be invoked with -u or it may convert the line terminators.

optional arguments:
  -h, --help            show this help message and exit
  -v                    show version information
  -q                    run (more) quietly
  -recurse              recurse into subdirectories
  -zip                  recurse into zip and tar files
  -nocontainer          disable deep scan of container documents, increases speed but may reduce accuracy with big files
  -pronom_only          disables loading of format extensions file, only PRONOM signatures are loaded, may reduce accuracy of results
  -input INPUT          file containing a list of files to check, one per line. - means stdin
  -filename FILENAME    filename if file contents passed through STDIN
  -useformats INCLUDEPUIDS
                        comma separated string of formats to use in identification
  -nouseformats EXCLUDEPUIDS
                        comma separated string of formats not to use in identification
  -matchprintf FORMATSTRING
                        format string (Python style) to use on match. See nomatchprintf, README.txt.
  -nomatchprintf FORMATSTRING
                        format string (Python style) to use if no match. See README.txt
  -bufsize BUFSIZE      size (in bytes) of the buffer to match against (default=131072 bytes)
  -container_bufsize CONTAINER_BUFSIZE
                        size (in bytes) of the buffer to match against (default=524288 bytes)
  -loadformats XML1,...,XMLn
                        comma separated string of XML format files to add.
  -confdir CONFDIR      configuration directory to load_fido_xml, for example, the format specifications from.

    Open Preservation Foundation (
    See License.txt for license information.
    Download from:
    Usage guide:
    Author: Adam Farquhar (BL), 2010
    Maintainer: Maurice de Rooij (OPF/NANETH), 2011, 2012, 2013
    FIDO uses the UK National Archives (TNA) PRONOM File Format
    and Container descriptions.
    PRONOM is available from


Any platform

  1. Download the latest zip release from
  2. Unzip into some directory
  3. Open a command shell, cd to the directory that you placed the zip contents into and cd into folder ‘fido’
  4. You should now be able to see the help text: python -h
  5. Before identifying files with FIDO for the first time, please update signatures first using the ‘’ script (see below for instructions).

Updating signatures

To update FIDO with the latest PRONOM file format definitions, run: python This is an interactive CLI script which downloads the latest PRONOM signature file and signatures. Please note that it can take a while to download all PUID signatures.

If you are having trouble running the script due to firewall restrictions, see OPF wiki:

Please note that this WILL NOT update the container signature file located in the ‘conf’ folder. The reason for this that the PRONOM container signature file contains special types of sequences which need to be tested before FIDO can use them. If there is an update available for the PRONOM container signature file it will show up in a next commit.


FIDO 1.0 and later will run on Python 2.7 with no other dependencies.

Format Definitions

By default, FIDO loads format information from two files conf/formats.xml and conf/format_extensions.xml. Addition format files can be specified using the -loadformats command line argument. They should use the same syntax as conf/format_extensions.xml. If more than one format file needs to be specified, then they should be comma separated as with the -formats argument.


Output is controlled with the two parameters matchprintf and nomatchprintf. Each is a string that may contain formating information. They have access to an object called info with the following fields:

printmatch: info.version (file format version X), info.alias (format also called X), info.apple_uti (Apple Uniform Type Identifier), info.group_size and info.group_index (if a file has multiple (tentative) hits), info.count (file N)

printnomatch: info.count (file N)

The defaults for FIDO 1.0 are:



It can be useful to provide an empty string for either, for example to ignore all failed matches, or all successful ones (see examples below). Note that a newline needs to be added to the end of the string using \n.


FIDO returns the following matchtypes:

  • fail: the object could not be identified with signature or file extension
  • extension: the object could only be identified by file extension
  • signature: the object has been identified with (a) PRONOM signature(s)
  • container: the object has been idenfified with (a) PRONOM container signature(s)

(In some cases multiple results are returned.)

Examples running FIDO

Identify all files in the current directory and below, sending output into file-info.csv

python -recurse . > file-info.csv

Do the same as above, but also look inside of zip or tar files:

python -recurse -zip . > file-info.csv

Take input from a list of files: Linux:

ls > files.txt
python -input files.txt


dir /b > files.txt
python -input files.txt

Take input from a pipe: Linux:

find . -type f | python -input -


dir /b | python -input -

Only show files that could not be identified.

python -matchprintf "" .

Only show files that could be identified.

python -nomatchprintf "" .

Deep scan of container objects

By default, when FIDO detects that a file is a container (compound) object, it will start a deep (complete) scan of the file using the PRONOM container signatures. When identifying big files, this behaviour can cause FIDO to slow down sigificantly. You can disable deep scanning by invoking FIDO with the -nocontainer argument. While disabling deep scan speeds up identification, it may reduce accuracy.

At the moment (version 1.0) FIDO is not yet able to perform scanning containers which are passed through STDIN. A workaround would be to save the stream to a temporary file and have FIDO identify this file.

License information

See the file LICENSE.txt for information on the history of this software, terms & conditions for usage, and a DISCLAIMER OF ALL WARRANTIES…