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

Annotations already cover read-only/idempotent/non-destructive safety, so the bar is lower. The description adds substantive behavior: the legal instrument and its correction, the year-dependent mark-up schedule (10%/20%/30%, fertilisers 1%), and the fallback return of candidate codes when no exact row exists.

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-loaded with purpose and unit, then the legal citation, mark-up schedule, and fallback in two tight sentences. Dense but every clause earns its place; no filler or restatement of the title.

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 no output schema, the description carries the return-value burden and does describe the unit (tCO2e per tonne) and the degraded return mode (candidate codes with descriptions). It could go slightly further on the candidate-code shape, but it is complete enough to call correctly.

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 quantifies the mark-up that the 'year' parameter drives (10% 2026 through 30% from 2028, fertilisers 1%), which the schema only labels as 'mark-up'. That meaning is not otherwise available from the schema.

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 precise verb+resource: returns the EU CBAM default value (tCO2e per tonne) for a CN8 code and country of production, including the legal source and mark-up regime. This clearly distinguishes it from siblings like estimate_cbam_cost or cbam_scope_check.

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?

Implicitly frames usage by naming the input keys (CN8 code, country) and describing the fallback path when the exact code has no row. However, it does not say when to prefer this tool over estimate_cbam_cost or cbam_scope_check, nor does it state prerequisites such as needing an importing year.

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