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

Annotations already declare the write/non-idempotent/open-world profile, so the description's job is to add context. It does: the booking triggers confirmation emails and calendar invites, which is a real externally-visible side effect an agent should anticipate. It does not discuss duplicate-booking 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?

Three tight sentences, front-loaded with the core action, then side effects, then prerequisites. No filler and nothing redundant.

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 7-parameter nested-object mutation with no output schema, the description covers the action, side effects, and the two prerequisite lookups, which is enough to invoke correctly. It omits what a successful response contains (booking ID/confirmation) and any guidance on the optional lengthInMinutes/metadata tradeoffs, leaving a small gap.

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 the schema already documents start, attendee sub-fields, guests, metadata, and lengthInMinutes in detail, including the find_available_slots hint. The description's only addition is where bookingFieldsResponses answers come from, which is marginal at this coverage level. 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 and resource ('Book a meeting') plus the scope constraint ('on one of the caller's event types for an attendee'), which separates it from sibling list_/get_/cancel_/reschedule_ tools. An agent can tell immediately that this is the creation path for a booking.

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?

Gives a concrete prerequisite chain: obtain a free start from find_available_slots, and pull required booking questions from get_event_type's bookingFields. It does not state exclusions (e.g. not for rescheduling or for other organizers' event types), so it stops short of a 5, but the when-to-use guidance is explicit.

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