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

Annotations only cover the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=true). The description adds genuinely non-obvious behavioral facts not derivable from them: this server suppresses confirmation/organizer notification e-mails but the event's own reminder and follow-up e-mails will later reach the address, and the e-mail must be unique per event. That is exactly the kind of consequence disclosure an agent needs before writing personal data.

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?

Three sentences plus an endpoint: the WRITE marker and the resource are front-loaded, and each sentence carries distinct information (scope, e-mail side effects, uniqueness). Slightly dense but no filler; the trailing endpoint line is arguably redundant with the tool's function.

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?

With no output schema and 100% schema coverage, the description's job is mainly to explain consequences and constraints, which it does. It covers scope, uniqueness, and e-mail behavior; it does not say what happens on a duplicate e-mail (error vs. update) or what identifying data comes back, which an agent might want for a non-idempotent write.

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 email, event_id, attending and rsvp_form_data; the enum and the nested form object are self-describing. The description echoes 'one e-mail address, personal data' and the uniqueness rule but adds no format, syntax or form-key guidance beyond what the schema states. 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 opens with a specific verb+resource and an explicit cardinality/scope: 'WRITE: adds ONE RSVP attendee (one e-mail address, personal data) to an event.' It even pins the underlying endpoint (POST /events/{id}/rsvps), which cleanly separates it from the sibling update/list/get RSVP tools.

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 gives a real condition for use rather than just a definition: 'only add someone who really RSVP'd.' That is a meaningful when-to-use constraint for a tool that will trigger downstream e-mails. It stops short of naming alternatives (e.g. update_rsvp_attendee for changing an existing response), so it is clear context without explicit routing.

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