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

Annotations already declare readOnlyHint, idempotentHint, non-destructive, and closed-world, which fully covers the safety profile for a pure arithmetic conversion. The description adds no behavioral context beyond that (no edge cases, no rounding/precision notes), but nothing is contradicted, so a 3 is appropriate given the low bar set by rich 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?

Short and front-loaded: the unit list and purpose come first, and it is easy to scan. The "Inputs: ..." and "Returns converted economy" clauses are largely redundant against the input schema and output schema, a minor waste but not enough to hurt readability.

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 simple, stateless conversion tool with full annotation coverage, a complete input schema, and an output schema, the description is essentially sufficient – the agent needs nothing more to invoke it correctly. The one real gap is not routing against the overlapping `convert_fuel_consumption` sibling.

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% and both unit parameters carry enums, so the schema fully documents the parameters. The description's "Inputs: value, from-unit, to-unit" merely restates them without adding format, constraint, or default semantics beyond what the schema provides – 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?

States a specific verb (convert) and resource (fuel economy units) and enumerates the four supported units, so the agent knows exactly what operation is performed. However, it never distinguishes itself from the near-identical sibling `convert_fuel_consumption` (nor `calculate_fuel_consumption`), which is the key differentiator an agent would need.

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?

"Use for car comparisons across regions" gives one implied usage context, which is better than nothing. But it provides no when-not guidance and no routing away from the confusingly similar `convert_fuel_consumption` sibling, so the agent must guess which of the two to call.

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