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

With no annotations, the description carries the burden well: it discloses the return envelope contents (provenance, publisher, source reference, retrieval date, licence, redistribution, verification) and the partial-failure contract (bad keys land in `not_found` rather than failing the batch). It does not cover rate limits, auth, or ordering guarantees, so not a full 5.

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?

Three tight sentences: the batch purpose and return shape come first, the alternative-routing instruction second, the edge-case behavior last. No filler.

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?

There is no output schema, yet the description still characterizes the response (audit envelope fields plus a `not_found` bucket), and the sole input is fully covered by the schema. Nothing needed to call this 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% and the only parameter's syntax, example keys, and 25-key cap are already documented in the schema. The description adds meaningful semantics about what happens to invalid keys, but no format details beyond the schema; baseline 3 applies.

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 and resource ('look up SEVERAL emission factors by key in one call') and immediately distinguishes itself from the singular sibling lookup_factor by emphasizing batch semantics.

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?

Explicitly says when to use this over the alternative: 'Use this instead of calling lookup_factor in a loop', and names concrete triggering scenarios (portfolio, multi-country comparison).

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