A Python tool to convert Zwift workout files (.zwo) to FIT workout files (.fit) for use with cycling computers and training platforms. Available as both a command-line tool and a web application.

This tool allows you to convert Zwift's proprietary workout format into the industry-standard FIT format, making your Zwift workouts compatible with Garmin, Wahoo, and other cycling computers that support structured workouts.

• Web Interface: Easy-to-use web application for drag-and-drop conversion
• Command Line Tool: Batch processing for advanced users
• Complete Workout Support: Handles all Zwift workout segments (Warmup, SteadyState, IntervalsT, Cooldown)
• Power Zone Conversion: Converts relative power zones to absolute watts based on your FTP
• Error Handling: Robust error handling with detailed feedback
• Preserves Metadata: Maintains workout names and structure
• Cross Platform: Works on Windows, macOS, and Linux

The easiest way to convert your ZWO files:

# Install dependencies
uv sync

# Start the web application
uv run python start_webapp.py

Then open your browser to http://localhost:5000 and:

1. Upload your .zwo file
2. Enter your FTP value
3. Click "Convert to FIT"
4. Download the converted file

For batch processing or automation:

uv run python zwift2fit.py

• Python 3.11+
• uv (recommended) or pip

git clone [repository-url]
cd zwift2fit
uv sync

git clone [repository-url]
cd zwift2fit
pip install -r requirements.txt

Start the web server:

uv run python start_webapp.py

Features:

• Drag & Drop Interface: Simply drop your .zwo file onto the upload area
• Real-time Validation: Instant feedback on file format and FTP values
• Secure Processing: Files are processed securely and cleaned up automatically
• Download Management: Converted files are automatically named and downloaded
• Error Handling: Clear error messages for troubleshooting

from zwift2fit import convert_zwo_to_fit

# Convert with default 250W FTP
convert_zwo_to_fit("my_workout.zwo", "my_workout.fit")

# Convert with custom FTP
convert_zwo_to_fit("my_workout.zwo", "my_workout.fit", ftp=275)

# Convert all .zwo files in current directory
uv run python zwift2fit.py

# The script will prompt for:
# - Input directory (default: current directory)
# - Output directory (default: same as input)
# - FTP value (default: 250W)

For production deployment:

# Build and run with Docker Compose
docker-compose up -d

# Or build manually
docker build -t zwift2fit-web .
docker run -p 5000:5000 zwift2fit-web

The web application also provides a REST API:

# Convert via API
curl -X POST http://localhost:5000/api/convert \
  -F "zwo_file=@workout.zwo" \
  -F "ftp=250" \
  --output workout.fit

The script converts relative power zones (e.g., 0.88 = 88% FTP) to absolute watts. Set your FTP appropriately:

# For a cyclist with 250W FTP
batch_convert_zwo_to_fit("./workouts", ftp=250)

# For a cyclist with 300W FTP  
batch_convert_zwo_to_fit("./workouts", ftp=300)

# Same directory (overwrites with .fit extension)
convert_zwo_to_fit("workout.zwo")

# Specific output path
convert_zwo_to_fit("workout.zwo", "converted/workout.fit")

# Batch with different directories
batch_convert_zwo_to_fit("./zwo_files", "./fit_files")

Input (.zwo file):

<workout_file>
  <name>Pacing1</name>
  <workout>
    <Warmup Duration="420" PowerLow="0.5" PowerHigh="0.75" />
    <SteadyState Duration="180" Power="0.88" />
    <IntervalsT Repeat="5" OnDuration="60" OffDuration="60" OnPower="0.9" OffPower="0.7"/>
  </workout>
</workout_file>

Output (.fit file):

• Warmup: 7 minutes ramping from 125W to 188W (avg 156W)
• Steady: 3 minutes at 220W (88% of 250W FTP)
• Intervals: 5x (1 min at 225W / 1 min at 175W)

your_project/
├── zwo_to_fit_converter.py    # Main script
├── zwift_workouts/            # Input directory
│   ├── workout1.zwo
│   ├── workout2.zwo
│   └── ...
└── fit_files/                 # Output directory
    ├── workout1.fit
    ├── workout2.fit
    └── ...

The script includes robust error handling:

• Invalid XML: Skips corrupted .zwo files and continues
• Missing Elements: Uses sensible defaults for missing workout data
• File I/O Errors: Reports errors but continues batch processing
• Progress Reporting: Shows conversion status for each file

"No .zwo files found"

• Check the input directory path
• Ensure files have .zwo extension
• Verify file permissions

"Error converting [file]"

• Check if the .zwo file is valid XML
• Ensure the workout structure follows Zwift format
• Try converting the file individually for detailed error info

FIT file not recognized by device

• Verify your FTP setting is reasonable (50-500W typically)
• Check that workout duration isn't too long for your device
• Some older devices may have limited FIT workout support

To verify conversion success:

1. Check that .fit files are created with reasonable file sizes
2. Import a test file into your cycling computer or training software
3. Verify power targets match expected values based on your FTP

The converter creates FIT files with these message types:

• FILE_ID: Identifies the file as a workout
• WORKOUT: Contains workout metadata (name, sport)
• WORKOUT_STEP: Individual workout segments with duration and power targets

Feel free to submit issues, feature requests, or pull requests. Common enhancement ideas:

• Support for additional ZWO elements (Cooldown, Ramp, etc.)
• Heart rate zone targets
• Cadence targets
• GUI interface
• More sophisticated FIT file validation

This project is provided as-is for personal use. The FIT file format is owned by Garmin/ANT+.

• Python: 3.6+
• Zwift: All .zwo workout file versions
• FIT Devices: Garmin Edge, Wahoo ELEMNT, and other FIT-compatible cycling computers
• Platforms: Windows, macOS, Linux