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

Annotations only declare the generic hint set (readOnlyHint=false, destructiveHint=false, idempotentHint=false), which is consistent with the description. The description adds genuinely non-derivable behavior: real slot is atomically reserved, confirmation is instant unlike book_room, and no payment is collected here (guest pays at the venue). This is meaningful operational context for money and reservation semantics.

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 dense sentences, front-loaded with the action and scope, followed by prerequisites and the two behavioral facts that matter (instant/atomic, no payment). No filler or restatement of the tool name.

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?

There is no output schema to replace, and the description covers the confirmation and payment model well. The remaining gap is the unlabeled identifier naming (restaurantId on a spa booking tool) and the fact that half the parameters get no semantic treatment, which an agent must infer.

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 only 25%, so the description must carry weight. It hints at guest semantics ('on behalf of a real guest') and points at check_service_availability for practitioner selection, but it never explains restaurantId vs serviceTypeId (venue/service identifiers for a spa), guestPhone (a required param), or guestEmail/notes — the remaining required parameters stay undocumented in both the schema and the description.

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+resource ('Book a ... SERVICE slot on behalf of a real guest') and immediately scopes it against siblings, naming check_service_availability, search_venues, and explicitly contrasting with book_room. An agent can distinguish it from book_reservation/book_room 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?

Gives an explicit prerequisite chain: use check_service_availability to find free slots, search_venues to obtain the venue's city/countryCode. It also states the differentiator vs the alternative (book_room) — instant vs presumably non-instant confirmation — which is exactly the routing information an agent needs.

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