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

Annotations only declare readOnlyHint=false and destructiveHint=false, so the description carries most of the behavioral burden and does well: it discloses that a real email is actually sent and that the recipient uses an embedded link to accept. The owner-only authorization requirement is also stated. It stops short of covering expiry/revocation behavior or failure modes, so not 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?

Two tight sentences with zero filler; the core action and the owner-only constraint are front-loaded, and the sibling-routing clause follows. Every clause earns its place.

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 4-parameter mutation with no output schema, the description covers the action, the side effect (real email + accept link), the authorization scope, and the sibling alternative. Nothing an agent needs to invoke it correctly is missing.

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%, and each parameter (role enum, email, tripId, expiresInDays with max 30) is documented in the schema itself. The description adds no parameter-level detail, so the baseline 3 applies.

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 (Email an invitation), the resource (collaboration on a trip), and the target (a named person), and explicitly contrasts with the sibling trip_share_create. An agent can distinguish it from trip_share_create and trip_collaborators_remove without opening any 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?

Names the alternative tool (trip_share_create) and the exact condition that selects it ('anonymous link with no particular recipient'), plus the owner-only restriction. Nothing about when to use this versus its sibling is left to inference.

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