Answers to the questions:
> - Read application code (written in python?) and extract an API specification? Is it flask only?
You can:
1. Construct schema objects and request objects using Python classes with marshmallow [1] library;
2. Split API paths (routes) into separate python modules, files for convenience and then add them in the `api/project.py` file.
> - Does it update the file on disk repeatedly?
No. You need to re-build the `api.yaml` file by yourself, using this command: "python build.py"
> - Does it modify generated application code to add an endpoint for the Swagger UI and host it?
No. You need to write the business logic of your API by yourself. For example, you write an API in Go and describe the API definitions (specifications) using my project just by adding new paths, schemas. Flask is used only for development purposes, it is not meant to create API using Flask, but you can do it as well.
> - Are any modifications to the pre-existing applications necessary?
No.
> - Does it wrap an existing application?
If you meant if this is a wrapper for other apps then it is. These two: marshmallow [1] and apispec [2]
If you meant if this wraps existed API then the answer is yes. You can describe existing APIs using my project.
> ... are there other tools in your space that do what you do, but differently?
Yes, a lot and for many languages. I can mention swagger-php [3], flask-swagger [4] which I know. But the two are using annotations in code (via docstrings) to describe the API definitions/specification when my project is meant to create ONLY API defs/spec.
[1]: https://marshmallow.readthedocs.io/en/stable/
[2]: https://github.com/marshmallow-code/apispec