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Your tools often need the same objects, like one database pool. You want to create them once and share them everywhere.

Whatever the lifespan yields becomes your shared application state, available to every tool, resource, and prompt.

Wrapping state in a dataclass gives you clear field names and editor autocomplete instead of guessing dict keys.

Inside the lifespan, construct each shared object and yield the container so it lives for the whole server run.

Shared state means one source of truth: every handler sees the same connection, so you avoid duplicate, leaking pools.

Skip module-level globals for connections. Passing state through context keeps tools testable and avoids hidden coupling.

App context is created once at boot, not rebuilt per request, so its objects persist across many tool calls.

Handlers do not import the state directly. They receive a context object at call time that exposes the yielded value.

Your shared container can hold more than clients: stash config like API base URLs or feature flags loaded at startup.

Treat shared state as mostly read-only. Mutating it from many concurrent calls invites subtle, hard-to-trace bugs.

Because the lifespan creates the state, it also owns tearing it down, so creation and cleanup stay in one tidy place.

What becomes the shared application state your handlers can use?

You build shared objects once in the lifespan, yield a typed container, and let every handler read it. Next: how to reach it. 🧩