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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds useful context—that it relies on the Carbon Interface API and returns emissions in grams, kg, and metric tons—but does not disclose potential errors, rate limits, or authorization requirements beyond the schema's _apiKey parameter. This is comparable to the calibration example where annotations cover safety and description adds moderate context.

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 three sentences: purpose, required inputs, and output units, followed by an example. Every sentence contributes valuable information, and the most critical details are front-loaded. It is appropriately concise without unnecessary elaboration.

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 a full output schema, 100% parameter coverage, and strong annotations, the description does not need to explain return structures or safety. It adds the external dependency (Carbon Interface) and output units, making it complete for an estimation tool. The absence of explicit sibling alternatives is a minor gap, but the description adequately contextualizes the tool's role.

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% with descriptions for all four parameters, so the baseline is 3. The description adds an example call that clarifies positional ordering and unit semantics, but it does not provide additional meaning beyond what the schema already conveys. The example array in the schema further reduces the need for extra parameter explanation.

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 tool's function: "Estimate CO2 emissions from driving a vehicle." It uses a specific verb and resource, and the phrase "driving a vehicle" distinguishes it from sibling tools like estimate_electricity and estimate_flight. The example call further reinforces the purpose.

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 provides a concrete example with arguments, implying how to use the tool. It mentions the prerequisite of a Carbon Interface vehicle model ID and shows the expected unit parameter. However, it does not explicitly exclude alternative tools or state when to prefer this over estimate_flight or estimate_electricity, though the scope is clear.

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