Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

destructiveHint=true is already declared, so the agent knows check-out carries a destructive profile. The description adds genuinely useful context beyond that: that checked_in=false reverses a prior check-in, and it exposes the underlying endpoint (POST /rpc/{accountId}/CheckInEventAttendee). It omits permissions, whether check-in triggers notifications, and side effects on guest counts.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

One tight sentence leads with the action and semantics before the guest case, with no padding. The trailing API endpoint is arguably operational detail rather than agent-facing guidance, a minor dilution.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a three-parameter mutation with full schema coverage and a destructiveHint annotation, the description plus schema gives an agent enough to invoke it correctly. There is no output schema to explain, though error and prerequisite behavior remains unstated.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so every parameter is already documented in the schema, including the guests-as-number constraint on checked_in_guests. The description only restates the boolean meaning, adding no format, default, or boundary detail beyond the schema, so the baseline of 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource: mark an event registration as checked in or undo it, with the exact boolean semantics inline. It is clearly distinguishable from sibling registration tools (list_event_registrations, create_event_registration) which read or create rather than toggle attendance state.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It explains what checked_in=true vs false do and that checked_in_guests applies only to guests-as-number registrations, which implies usage. However it never states prerequisites or exclusions (e.g. event must be in progress, registration must be confirmed), and names no alternative tool.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.