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

Annotations already declare it is a non-readonly, non-idempotent, open-world write. The description adds meaningful behavior beyond that: the call returns a payment link, payment is online in full, and nothing is secured until paid. It does not cover failure modes or what happens if the link expires, but it substantially enriches the mutation 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 short sentences, front-loaded with the action and outcome, then the gating condition, then the payment caveat. Every sentence carries distinct information with no padding.

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 16-parameter, no-output-schema booking mutation, the description covers the return value (payment link) and the critical preconditions, and the schema handles the rest including duplicate confirmation. It lacks detail on what happens after payment or on failed bookings, but is adequate to call 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 75%, so the schema documents most fields itself. The description restates the fields the agent must confirm (route, date, time, passengers, total) but adds no per-parameter meaning beyond what the schema already carries, so 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 (Book) and resource (one ferry or speedboat departure) plus the outcome (secure payment page). It explicitly ties itself to search_transfers as the source of the listing, so an agent can distinguish it from search_transfers and book_experience immediately.

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 clear precondition: book only after the traveller explicitly approved the restated route, date, time, passengers and total, and only for a departure surfaced by search_transfers. No explicit when-not or alternative tool is named, but the usage context is unambiguous.

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