lookup_factor

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

With no annotations provided, the description carries the full burden and does so thoroughly. It discloses what is returned (value plus audit envelope), details provenance and verification fields, and explains the missing-key fallback behavior with candidate keys.

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 sentences, each earning its place: operation, return envelope details, and usage guidance. The most important information is front-loaded in the first sentence, and the detail is dense but not bloated.

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?

Despite no output schema and no annotations, the description is complete for a single-parameter lookup tool. It explains the return shape, provenance and verification details, error behavior, and when to use the sibling tool, leaving no critical ambiguity.

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% for the single 'key' parameter, including an example. The description reinforces that the lookup is by 'canonical key' but does not add substantial parameter semantics beyond the schema, so the baseline of 3 is appropriate.

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 uses a specific verb and resource: 'Look up a single greenhouse-gas emission factor by its canonical key.' It also distinguishes itself from siblings by explicitly directing users to search_factors when the key is unknown, and describes the narrow lookup scope versus broader search/calculation tools.

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?

Explicit guidance is provided: 'Use search_factors first if you do not know the key.' This clearly states when this tool is appropriate and names the alternative, which is exactly the kind of usage guidance expected.

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