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

Annotations already declare destructiveHint=true, so the description adds little side-effect context beyond that. It does not disclose that registration may create/update invoices with fees, whether duplicate registrations error, what permissions are required, or that it is a POST mutation with real-world consequences for the contact.

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 front-load the core action and scope, with no filler. The trailing endpoint string ('Wild Apricot: POST /accounts/{accountId}/eventregistrations') is marginally useful but not essential for an agent.

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 mutation with 8 params, no output schema, and thin annotations, the description covers what the tool does and the key prerequisite, which is enough to invoke it. It is not complete on behavioral risk (fees, invoicing, failure modes) that an agent should know before writing.

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 (memo, on_waitlist, show_to_public, recreate_invoice, registration_fields) is already documented in the schema. The description adds only the cross-reference for registration_type_id, which is baseline-level value.

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') plus the scope constraint ('under one registration type'), which cleanly separates it from create_contact, check_in_attendee, and list_event_registrations in the sibling set. The explicit pointer to wildapricot_list_event_registration_types pins down where registration_type_id comes from.

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 surfaces a required upstream call (wildapricot_list_event_registration_types) and mentions the waitlist variant, which is useful routing context. However it never states when NOT to use this tool (e.g., vs check_in_attendee or create_contact) nor prerequisites such as the contact/event already existing, so usage is implied rather than spelled out.

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