A small pure Python script that converts API specifications (OpenAPI/Swagger) into UML diagrams. Supports both PlantUML and Mermaid output formats. The goal is not to replace existing documentation generators, but to complement them with a visual representation of the routes, models, and their relationships.
To create a PlantUML diagram from the petstore example, call the script with:
python bin/swagger_to_uml petstore_example/swagger.json > petstore_example/swagger.puml
It will create the file petstore_example/swagger.puml which can then be translated into a PNG image with PlantUML with:
plantuml petstore_example/swagger.puml -tpng
Note you need to install PlantUML and Graphviz for this.
To generate a Mermaid diagram instead, use the -f mermaid option:
python bin/swagger_to_uml petstore_example/swagger.json -f mermaid > petstore_example/swagger.mmd
Mermaid diagrams can be rendered directly in many Markdown viewers (GitHub, GitLab, VS Code, etc.) or using the Mermaid CLI.
- Supports Swagger 2.0 and OpenAPI 3.x.
- Input can be JSON or YAML; format is auto-detected. For YAML files,
PyYAMLis required.
- PlantUML (default): Traditional UML diagram format requiring PlantUML tooling.
- Mermaid: Modern diagram format with native support in many platforms.
The script runs with Python 3. For YAML input, PyYAML is required. Transforming PUML into vector graphics or other requires external tools however.
On macOS, the installation of the required tools with Homebrew is simple:
brew install plantuml graphviz
python bin/swagger_to_uml [-h] [-f {plantuml,mermaid}] input_file
positional arguments:
input_file Path to Swagger/OpenAPI specification file (JSON or YAML)
options:
-h, --help show this help message and exit
-f, --format {plantuml,mermaid}
Output format: plantuml (default) or mermaid
The tool can also be used as a Python library:
from swagger_to_uml import parse_file, PlantUMLRenderer, MermaidRenderer
diagram = parse_file("api_spec.json")
plantuml_output = PlantUMLRenderer().render(diagram)
mermaid_output = MermaidRenderer().render(diagram)To convert PlantUML diagrams to SVG:
# Using PlantUML CLI
plantuml diagram.puml -tsvg
# Or using the Java jar directly
java -jar plantuml.jar diagram.puml -tsvgTo convert Mermaid diagrams to SVG:
# Install Mermaid CLI
npm install -g @mermaid-js/mermaid-cli
# Convert to SVG
mmdc -i diagram.mmd -o diagram.svg
# Convert to other formats
mmdc -i diagram.mmd -o diagram.png
mmdc -i diagram.mmd -o diagram.pdf- PlantUML: PlantUML Online Server
- Mermaid: Mermaid Live Editor
The script is tested with pytest. Install dependencies and run tests:
pip install -r requirements.txt
python -m pytest -qThe script is just a first proof-of-concept version. Issues and pull requests welcome!
MIT License
Copyright (c) 2017 Niels Lohmann http://nlohmann.me
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.