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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description adds useful output context that annotations cannot convey – the returned value includes a reference chart for 4–12 L/100 km – but says nothing about rounding, precision, or the result payload shape.

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?

A single front-loaded sentence delivers the conversion scope, a concrete example, and the returned chart in sequence. It is efficient, though the trailing URL is low-value for an agent deciding whether to call the tool.

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 does the necessary work of signaling what comes back (a converted value plus a reference chart). For a two-parameter, zero-required, read-only conversion tool this is close to sufficient, with only precision/rounding behavior left unaddressed.

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 worked example ('30 mpg (US) is 7.84 L/100 km and 36.03 imperial mpg') incidentally illustrates the 'mpg-us' vs 'mpg-uk' enum semantics, but it does not explain the 'l100'/'kml' options or the valid range of 'value' beyond what the schema already states.

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 names a specific verb and resource ('Convert mpg to L/100km, km/L or UK mpg') and enumerates the exact supported target units, so an agent knows precisely what the tool computes. It does not, however, distinguish itself from the sibling unit_converter, which also handles unit conversions.

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?

There is no explicit when-to-use guidance, no prerequisites, and no statement of when a different tool (e.g., unit_converter or fuel_cost_calculator) would be preferable. Usage is only implied by the conversion example.

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