A transit authority needs a city API tool that built-in Copilot does not provide. Which use case applies?

When a transit authority needs a city API tool that built-in Copilot does not provide, the sound use case is to create or use a custom agent that can call that city API. Custom agents extend Copilot with tools and actions—API calls for vehicle location, fare exceptions, or service alerts—when out-of-the-box Copilot lacks that integration. That is the fundamentals reason to choose an agent over hoping built-in chat invents API access.

Using Microsoft 365 Copilot Chat to call the city API when built-in Copilot lacks that action fails because built-in chat cannot invent the missing API tool on its own and still lacks that integration without a custom agent. Building a declarative agent in Copilot Studio that calls the city API through web search grounding fails by concept: web search grounding only retrieves public information and cannot invoke the live municipal API as a tool action. Creating a Power Automate flow that calls the city API to send scheduled emails outside Copilot chat fails because it runs as standalone automation outside Copilot and does not extend built-in Copilot with the API tool the scenario requires.

Exam caveat: Agents that call municipal APIs must use secured authentication, least-privilege app permissions, and logging. Exam items test the idea of extending with tools/agents, not writing the API code.

Operational check: Identify the city API Copilot cannot call natively, register an agent tool against a non-production endpoint with proper Entra app credentials, and verify the agent can invoke it while web search grounding alone gives a declarative agent no ability to call the API.