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

With no annotations, the description carries the disclosure burden and does well: it enumerates the returned fields (key, name, section, value, unit, gas) and states the results are sufficient to choose between factors or read numbers "without a second call." It omits anything about ranking, case sensitivity, or pagination behavior beyond the limit param, which keeps it short of a 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, front-loaded with the core verb and resource; the return-value note and the sibling routing each earn their place with 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?

No output schema exists, and the description compensates by describing the return payload, so return values need not be invented by the agent. With alternatives routed and all four params schema-documented, 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 description coverage is 100%, so the baseline is 3. The description restates the three filter modes (section, key prefix, free text) that the schema already documents, adding no syntax, format, or combination semantics beyond it.

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 ("Find emission factors") plus the three lookup modes, and explicitly distinguishes itself from lookup_factor/lookup_factors. An agent can identify this as the discovery/browse tool without opening any schema.

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?

Names the alternatives explicitly and gives the selecting condition: use this to browse/preview, call lookup_factor for one factor's full audit envelope, lookup_factors for several. Both the when-to-use and when-to-use-something-else are stated.

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