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

By Open Preservation Foundation

Build Status Code Coverage

FIDO is a command-line tool to identify the file formats of digital objects. It is designed for simple integration into automated work-flows.

FIDO uses the UK National Archives (TNA) PRONOM File Format and Container descriptions. PRONOM is available from See LICENSE for license information.


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 ...]]

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.


(also see:

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
  4. Run python install to install FIDO and dependencies. This may require sudo on Linux/OSX or admin privileges on Windows.
  5. You should now be able to see the help text: fido -h

Using pip

  1. Run pip install opf-fido This may require sudo on Linux/OSX or admin privileges on Windows.
  2. You should now be able to see the help text: fido -h

Updating signatures

To update FIDO with the latest PRONOM file format definitions, run: fido-update-signatures 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 through 1.3.3 will run on Python 2.7 with no other dependencies.

FIDO 1.3.4 and later requires the python dependency 'olefile'. This can be installed using pip install olefile, by running python install, or a pip installation will handle dependencies.

FIDO 1.3.3 and later have experimental Python 3 support.

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:

  • printmatch:

  • "OK,%(info.time)s,%(info.puid)s,%(info.formatname)s,%(info.signaturename)s,%(info.filesize)s,\"%(info.filename)s\",\"%(info.mimetype)s\",\"%(info.matchtype)s\"\n"

  • printnomatch:

  • "KO,%(info.time)s,,,,%(info.filesize)s,\"%(info.filename)s\",,\"%(info.matchtype)s\"\n"

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:


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 -

Windows: 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...

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