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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false), but the description adds substantial operational context: counts are live, only active guests are included, removed guests are excluded, each guest counts once under one status, and plus-ones are folded into adults_going/kids_going party sizes. It also discloses that the public RSVP link is only returned after publication.

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?

Front-loaded with the triggering scenario, then metric semantics, then prerequisite, then the sibling alternative. Six tight sentences with no filler; every clause carries information the agent needs.

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?

An output schema exists so return structure needn't be explained, yet the description still defines what the returned counts mean (party-size inclusion, active-only scope, single-count rule), which is exactly the context needed to interpret the numbers correctly.

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 coverage is 100% so the baseline is 3, and the description goes beyond it by warning that event_id is the event's id, not a guest invitation_id, and by pointing to lemonvite_list_invitations as the source. It does not add format/syntax detail, but the disambiguation is genuinely useful.

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 ('counts how many guests are going, declined, maybe or have not replied') and explicitly disambiguates from lemonvite_list_guests ('To see which guest said what'). An agent can select it without opening either schema.

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 concrete triggering user question, names the alternative tool and the condition that selects it, and states the prerequisite for obtaining event_id from lemonvite_list_invitations. When-to-use, when-not, and alternative are all present.

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