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

Annotations already cover safety (readOnly, idempotent, non-destructive, openWorld), so the bar is lower. The description still adds real behavioral context beyond them: output is a EUR range with per-country breakdown, and it flags partial results when a country on the route lacks data — an important caveat an agent should relay. It does not mention latency or rate limits, so not a 5.

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 tight sentences with zero padding: capability and output first, the partial-data caveat second, the routing constraint last. No restatement of the title and nothing that could be cut without losing information.

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?

An output schema exists, so return-value structure need not be explained, and annotations carry the safety profile; the description supplies output granularity and the partial-result caveat. Slightly incomplete in not indicating that a country waypoint resolves to its capital (left to the schema) or roughly how partial results appear, but nothing an agent needs to call it correctly is missing.

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 waypoint limits, the locale behavior, and the vehicle_class enum/default are fully documented in structured fields. The description mostly restates the 2-10 place-name bound already in the schema and adds no meaning for vehicle_class or locale. Baseline 3 applies when the schema does the heavy lifting.

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 ('Estimate toll cost for a road trip'), the input shape (2-10 place names), and the output form (EUR range with per-country breakdown). It also names the sibling it is not — plan_road_trip — so the agent can distinguish the two without opening schemas.

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?

Explicit routing: 'Use it only for the toll cost between named places when no other trip details are asked; for a whole trip use plan_road_trip.' Both the when and the when-not with a named alternative are present.

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