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

Annotations are thin (only destructiveHint=true), so the description carries most of the burden. It adds the prerequisite that the contact must already exist and surfaces the underlying POST endpoint, but says nothing about duplicate registrations, permission/auth requirements, or the invoice side effect that recreate_invoice triggers.

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?

Two tight sentences plus one API-path line; the core action and its prerequisite lead, and the waitlist alternative follows. No filler or restatement of the title.

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 an 8-parameter create tool with full schema coverage and no output schema, the description covers the main flow, the required prerequisite tool, and the waitlist variant. It leaves out edge-case behavior (duplicate handling, missing/closed registration type errors) but is otherwise adequate for correct invocation.

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. The description only echoes two of them (registration_type_id, on_waitlist) and adds no format, default, or interaction details beyond that baseline.

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 ('Register an existing contact for an event') and adds the key constraint that exactly one registration type applies. It also names the sibling tool that supplies registration_type_id, letting an agent distinguish it from list_event_registrations and check_in_attendee without opening schemas.

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?

Points to wildapricot_list_event_registration_types as the source of a required id and notes that a waitlist entry is an alternative outcome, which is useful routing context. However, it gives no when-not guidance (e.g., what to do if the contact is already registered, or how this relates to check_in_attendee).

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