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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the description only needs to add context, which it does: it discloses that the tool checks farm opening hours on arrival and computes booking needs, and describes what is returned. It does not mention failure behavior when a farm is closed, but the added behavioral detail is meaningful.

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 sentences, both front-loaded with the core action and the operational detail. No filler; every clause conveys behavior the agent needs.

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?

Despite nine parameters, a nested start object and no output schema, the description conveys the return contents (arrival times, distances, booking needs) and the two operating modes. Remaining gaps, such as closed-farm handling or route-failure behavior, are minor for a read-only planner.

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 56%, and the description adds real value for one gap by explaining that farm_ids can be left empty to auto-pick via area. However, several parameters (start_time, stops, road_factor, avg_speed_kmh, minutes_per_stop) are only documented in the schema and get no additional meaning from the description. A baseline 3 is appropriate given partial coverage.

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 ('Plans a self-drive winelands day') and enumerates the concrete operations: ordering farm visits, checking opening on arrival, and returning arrival times, distances and booking needs. This clearly separates it from the sibling lookup tools (get_wine_farm, search_wine_farms), which retrieve rather than plan a route.

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 final sentence explicitly resolves the main decision: 'Pass farm ids, or leave empty to auto-pick farms in an area,' tying each mode to its trigger. It gives clear context but does not name alternatives or state when-not to use this tool versus search_wine_farms.

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