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

Annotations only declare readOnlyHint and openWorldHint; the description adds materially more: the output unit (kg CO2e per matching factor), the payment requirement ($0.002 USDC via x402 on Base/Solana/Arc), and that failed calls are not charged. That billing/auth disclosure is exactly the kind of behavior an agent cannot infer from structured fields.

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?

Front-loads the computation and mode list, then the factor-source caveat, then pricing — a sensible order with no filler. The opening sentence is dense (formula, factor provenance, and eight modes in one breath), which slightly hurts scanability.

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?

With an output schema present, return values need not be explained, and annotations cover the safety profile. The description still supplies the remaining essentials: methodology source, unit, mode coverage, and cost model — enough for an agent to call it correctly on the first attempt.

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 100%, so a 3 is the floor; the description exceeds it by explaining how the parameters combine into the result and by naming the factor families that 'mode' and 'type' select from. It still does not clarify what happens if 'type' matches no published row.

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 the exact resource (freight CO2e emissions for a shipment) and the computation (tonnes × km × DESNZ 2025 factor), enumerating the supported modes. No sibling computes shipment emissions, and the description preempts confusion by naming the GLEC tool it is not.

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 clear context for when this applies — any shipment whose emissions must be computed with UK DESNZ/GHG Protocol factors — and explicitly distinguishes itself from the GLEC tool. It stops short of naming a sibling alternative or stating exclusions (e.g., non-UK factor regimes).

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