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A FIT file parsing and decoding library written in Python3 (>= 3.6).

Usage Example

Read a FIT file, frame by frame:

import fitdecode

with fitdecode.FitReader('') as fit:
    for frame in fit:
        # The yielded frame object is of one of the following types:
        # * fitdecode.FitHeader (FIT_FRAME_HEADER)
        # * fitdecode.FitDefinitionMessage (FIT_FRAME_DEFINITION)
        # * fitdecode.FitDataMessage (FIT_FRAME_DATA)
        # * fitdecode.FitCRC (FIT_FRAME_CRC)

        if frame.frame_type == fitdecode.FIT_FRAME_DATA:
            # Here, frame is a FitDataMessage object.
            # A FitDataMessage object contains decoded values that
            # are directly usable in your script logic.

Command line utilities

fitjson exports JSON:

$ fitjson --pretty -o out_file.json

To ease the introspection or your FIT files, fittxt exports to a dedicated TXT format:

$ fittxt -o out_file.txt

Both commands accept a --filter option (or -f) which can be specified multiples times:

$ # include only RECORD messages:
$ fitjson -f=record -o out_file.json

$ # exclude FILE_ID and EVENT messages:
$ fitjson -f=-file_id -f=-event -o out_file.json


fitdecode is available on PyPI:

$ pip install fitdecode

Or, to get the latest working version, you can clone fitdecode's source code repository before installing it:

$ git clone
$ cd fitdecode
$ python test     # optional step to run unit tests
$ python install

Note that for convenience, the cmd directory located at the root of the source code tree can safely be added to your PATH, so that fitdecode commands can be called without the package to be installed.


fitdecode is a non offensive and incompatible rewrite of the fitparse library, with some improvements and additional features, as well as efforts made to optimize both speed and memory usage.

Main differences between fitdecode and fitparse:

  • fitdecode's API is not compatible with fitparse's
  • fitdecode requires Python version 3.6 or greater
  • fitdecode is faster
  • fitdecode allows concurrent reading of multiple files by being thread-safe, in the sense that fitdecode's objects keep their state stored locally
  • fitdecode does not discard the FIT header and the CRC footer while iterating a file, which allow to get a complete 1:1 representation of the file that is being read
  • This also allows the client to easily deal with so-called chained FIT files, as per FIT SDK definition (i.e. concatenated FIT files)
  • CRC computation and matching are both optional. CRC can be either matched, or only computed, or just ignored for faster reading.
  • fitdecode offers optional access to records, headers and footers in their binary form, to allow FIT file cutting, stitching and filtering at binary level

Why a new library?

A new library has been created instead of just offering to patch fitparse because many changes and adds in fitdecode break fitparse's backward compatibilty and because it allowed more freedom during the development of fitdecode.


Documentation is available at


This project is distributed under the terms of the MIT license. See the LICENSE.txt file for details.


fitdecode is largely based on the generic approach adopted by fitparse to define FIT types and to decode raw values. That includes the module and all the classes it refers to, as well as the script