An emergency-management agency wants its incident-response agent to trigger alerts on a legacy siren and notification system that predates any modern API standard. No prebuilt MCP server or existing Google Cloud integration covers this system. When does building a custom MCP server for it make sense?
Select an answer to reveal the explanation.
Short Explanation
Think of a custom MCP server like building a translator for a language nobody else speaks yet: when the legacy siren system has no existing prebuilt connector and no modern API standard to plug into, someone has to build that bridge before an agent can call it at all. That's exactly the situation that justifies the custom build - not a system that's already API-ready, not a preference for self-hosted infrastructure on its own, and not a one-off test call.
Full Explanation
Building a custom MCP server is justified when a gap exists: no prebuilt MCP server or existing Google Cloud integration reaches the target system, yet agents still need a standardized way to call it, which is exactly the legacy siren and notification system's situation here - it predates modern API standards, so nothing off-the-shelf covers it. If the legacy system already exposed a modern REST API, that changes the calculus significantly; an existing API doesn't automatically need a custom MCP server built around it, since simpler integration paths or an existing connector might already reach it. Wanting to keep an integration entirely within agency-controlled infrastructure is a legitimate architectural preference in some cases, but it isn't what makes a custom MCP server necessary here - the deciding factor is the coverage gap, not a hosting preference, and an agency could have that same preference for a system a prebuilt connector already covers. And building integration infrastructure for a single anticipated test call is disproportionate effort; a one-off need doesn't justify building and maintaining a standardized server meant for repeated agent use. The scope caveat: building a custom MCP server is an investment that pays off when the integration will be reused across agents or over time, not for a single isolated call. A concrete check: confirm no existing MCP server catalog entry or Google Cloud connector already reaches the legacy system before committing engineering time to building one from scratch.