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

Annotations already declare readOnly/idempotent/openWorld=false, and the description still adds context beyond them: no side effects, no network access, no stored state, deterministic output, and concrete limits (64 KB input, 1 s per call, 1 MB result). Those limits and the determinism guarantee are operationally useful and not present in the structured fields.

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 the purpose and then cleanly labeled When / Not for / Side effects / Deterministic / Limits, so an agent can skim. It is duplicated in Spanish and English, roughly doubling length, which costs a little but the content is non-redundant per language.

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 3-parameter pure conversion tool with a full output schema, the description covers purpose, scope, exclusions, safety profile, determinism and operational limits. Nothing an agent needs to call it correctly or set expectations about the response 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 'value', 'from', 'to' and the omit-for-all behavior are already documented in the schema. The description nevertheless adds real meaning by naming the supported unit tokens and flagging the inverse relationship for L/100 km, which changes how an agent should interpret and present results.

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 (converts fuel economy) and enumerates the exact unit set (km/L, L/100 km, US mpg, imperial mpg), plus calls out the inverse relationship for L/100 km. It also names the sibling it is not (convert-volume), so an agent can separate it from the other convert-* tools in the list.

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 'When:' clause scopes use to conversions with exact definitional factors, and an explicit 'No para / Not for:' clause routes volume conversion to convert-volume. Both the include and exclude conditions are stated, which is the strongest form of routing guidance.

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