Various embodiments disclose an in-message application facilitating the use of third-party application programming interfaces (APIs). In particular, these in-message applications (referred to as “cards”) may be designed by a developer to access third-party API functionality. A user may then create a message referencing, e.g., a web address associated with the developer's card. The system may receive the user's message and recognize the reference. The system may then distribute an instantiation of the card to various recipients, the instantiation including elements generated using, or providing the user access to, the third party functionality.