The definition and all resources are at www.tsapi.net
An extensive demo survey covering all question types & loops is here: https://data.bayesprice.com/s3/TSAPI-Demo-1
That link to the survey also contains a PDF Questionnaire & flat example data / meta data file in Excel.
The TSAPI definition can be found on Swagger here.****
Access the GitHub repository here.
Here's a NuGet package containing the object model (defining the public classes and interfaces) for TSAPI.