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

Annotations already declare destructiveHint=true, so the primary behavioral warning is covered structurally; the description's 'or undo it (false)' clarifies which branch is the state-reverting one, which is useful. However, it adds no detail on permissions, whether re-checking-in is idempotent, or how guest counts interact with the registration total. With annotations carrying the safety profile, a 3 is appropriate.

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?

A single sentence front-loads the core action, then covers the toggle and the guest edge case, with the endpoint appended last. Nothing is repeated or padded.

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 simple toggle with full schema coverage and no output schema, the description covers the essential behavior, but omits any statement of permissions/auth requirements or what the call returns on success or failure. Adequate but with clear gaps for a state-mutating operation.

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 the schema already documents all three parameters, including the true/false meaning of checked_in and the guests-as-number condition. The description largely restates those semantics ('for anonymous guests') rather than adding format or constraint detail. Baseline 3 applies when the schema does the heavy lifting.

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?

The description states a specific verb and resource ('Mark an event registration as checked in or undo it') and maps both boolean values to their effect, so the agent knows exactly what the tool mutates. It also records the underlying Wild Apricot RPC endpoint, anchoring the operation. No sibling tool performs check-in, so there is no ambiguity to resolve.

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 clearly says when to pass checked_in=true versus false, and calls out the guest-count case, which tells the agent which parameter to reach for. There are no alternative tools to compare against, and no exclusions or preconditions (e.g., event must exist, registration must not be cancelled) are stated.

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