JAX-RS
The AppBuilder supports the JAX-RS standard for developing REST endpoints.
The generated URL will resemble the following format:
Root
../services/sdk/platform/jaxrs/[partnerID]/[appname]/[modulename]/[service]
SDK
../sdk/platform/jaxrs/[partnerID]/[appname]/[modulename]/[service]
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After installing an app, its JAX-RS resources are shown in:
•    Apps TSI > Technical info tab: all resources of all modules.
•    Apps > Details > Artifacts > Technical info: endpoints only.
Root vs. SDK
ROOT is stateful and SDK is stateless. As a result, if the app is meant for end users, you want it to be stateful and the developer should use Root.
If the app is meant for system integration, it can be stateless and your developer would need to use SDK.
For more (technical) information about this topic, see the developer portal (login required).