The objective of this study was to investigate the state of the interoperable mobile health application (app) ecosystem at the start of the 21st Century Cures Act to understand the opportunities currently available to patients for accessing and using their computable clinical data. Thus, we sought to identify third-party apps in the Apple App and Google Play Stores that seem to be capable of automatically downloading clinical data via a FHIR-based application programming interface through a targeted review of health apps. We found that few of the apps in this review have this capability (1.4% of 1,272 iOS apps and 0.6% of 1,449 Android apps). Ultimately, our results suggest that this is a nascent marketspace. If barriers to app development are not identified and addressed, and efforts are not made to educate patients and improve discoverability of apps, it could mean that patients will not benefit from these interoperability measures.