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

No annotations are provided, so the description carries the full burden. It only reveals the side effect of incrementing num_days and the auth requirement, but omits many behavioral traits: whether the operation is reversible, what happens if the itinerary_id is invalid, whether it mutates other state, or any response format. For a mutation tool with zero annotations, this is insufficient.

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?

The description is a single concise sentence that communicates the primary action and a key side effect, with no extraneous information. However, it could be restructured to front-load the required auth context more clearly.

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?

Given the tool has no output schema, no annotations, and 3 parameters with low schema coverage, the description leaves significant gaps. It does not state what the operation returns (e.g., the updated itinerary object), error conditions (e.g., missing itinerary), or any rate limits. For a tool that mutates state (incrementing num_days), these are critical missing details.

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 low (33%), but the description does not add any parameter-specific details beyond what the partial schema provides. The tool name, title, and schema already convey that itinerary_id is required and that title is optional. The description does not explain the notes parameter at all, nor does it clarify the relationship between notes and title. Since the description fails to compensate for the low schema coverage, it merits a baseline 3.

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?

The description clearly states the action ('append an extra day') and the resource ('concierge itinerary'), and mentions a specific side effect ('increment num_days'). It distinguishes itself from sibling tools like add_activity and write_itinerary_day_detail by focusing on adding a day rather than adding an activity or writing day details.

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?

The description mentions a prerequisite ('requires a bearer token') but does not specify when to use this tool versus alternatives like create_itinerary or update_itinerary. There is no guidance on when not to use it, such as if the itinerary already has a maximum number of days or if the user only wants to modify an existing day.

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