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

Beyond the readOnly/idempotent annotations, it discloses the key hidden behavior: when carbon_price is omitted, the tool falls back to the latest EU ETS EUA spot snapshot and cites it in the output. It also states the emission intensity is caller-supplied data rather than the service's own, which materially changes how the result should be trusted.

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?

Labeled sections (Purpose / Guidelines / Limits / Ex) make it scannable and the core formula is front-loaded. The Limits paragraph is dense but every clause carries a material caveat, so it is only mildly longer than needed.

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 calculation tool with an output schema already covering the return payload, the description supplies everything else an agent needs: inputs, the default-price behavior, scope exclusions, and example calls. Nothing required to invoke or interpret the tool 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 coverage is 100%, so the baseline is 3, but the description adds units and provenance semantics (tCO2e per tonne, tonnes, optional price with a cited fallback) plus two concrete example invocations that disambiguate argument meaning. It slightly exceeds what the schema alone conveys.

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 states a precise verb+resource and even the formula ('embedded emissions multiplied by a carbon price'), which uniquely separates it from siblings like compare_carbon_prices or get_cbam_timeline. An agent can tell instantly what it computes and what it does 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?

It gives explicit usage context ('order-of-magnitude questions about CBAM exposure') and a clear exclusion zone (not a declarable amount, excludes free-allocation and third-country deductions, not advice). It stops short of naming a sibling tool for the declarable calculation, so routing is implied rather than explicit.

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