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

Annotations declare readOnly=false, destructive=false and idempotent=false, so the mutation and safety profile is partly covered. The description adds genuine behavioral context beyond that: the ordering relationship to option-type tools, that destinations are the anchor objects options attach to, and that isReturnToHome is pinned to the end. It doesn't mention permissions or return identity, but it adds real value over the annotations.

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, front-loaded with the core action and scope, followed by the ordering prerequisite and the special-case parameter hint. Every sentence carries information an agent needs to call it correctly.

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 mutation tool with no output schema, the safety profile is covered by annotations and the description supplies the workflow ordering and isReturnToHome semantics. What is missing is what the call returns and how the newly added destination is identified for follow-up calls (e.g. update_destination), so it is strong but not fully complete.

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%, so the baseline is 3. The description goes slightly beyond by giving usage meaning to isReturnToHome ('for the final leg home') and tying the destination data to itinerary order, which reinforces how startDate/endDate fit. It adds a little but leaves most parameter detail to the schema.

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 ('Add a place the traveller will stay at within a variant') and clarifies the domain concept with a concrete example ('Lisbon, Portugal'). It also distinguishes destinations from the option-type siblings by explaining that accommodation, transport and getting-around options attach to destinations.

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 explicit ordering guidance: 'add these before adding options' and 'Set isReturnToHome for the final leg home.' This tells the agent both the sequencing prerequisite and a special-case parameter usage. It stops short of naming a specific alternative sibling or stating when not to use it, so it is not a full 5.

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