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

Annotations cover the write/external/reversible profile, and the description adds real beyond-schema context: messages are delivered privately so guests never see each other's addresses, there is no message cap, per-call confirmation is on by default, and a Cotlet API key with app access is required. The privacy point is stated twice and error/failure behavior is unaddressed, which keeps it from a 5.

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?

The purpose is front-loaded and the sequence is logical, but the privacy guarantee is stated twice ('Each guest gets it privately' and 'guests never see each other's email addresses'), and the confirmation/API-key sentences are operational boilerplate that could be tightened.

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 four-parameter messaging action with no output schema, the description covers scope, privacy semantics, confirmation policy and auth requirements well. It stops short of describing failure or partial-delivery behavior, so it is strong but not exhaustive.

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, but the description adds genuine meaning: it clarifies guest_id is an alternative to group rather than an additional filter, and glosses no_reply as 'still no response' and group default as all. That is more than the schema alone conveys.

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 ('Send a message to a group by RSVP status or to one guest') and immediately scopes the operation. An agent can distinguish this from evite_send_invitation and evite_update_guest_rsvp because the description makes clear this pushes a private message rather than an invitation or an RSVP mutation.

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?

Explains the two calling modes ('To write to one guest, pass guest_id', otherwise a group) and gives an operational instruction ('confirm with the user before each call'). It does not explicitly contrast against sibling tools such as evite_send_invitation, but the usage context is clear enough to act on.

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