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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the bar is lower. The description still adds real value: it discloses the return shape (converted value plus normalized unit names) and the hard constraints (no currency, same-dimension requirement).

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, front-loaded with the core purpose, then usage framing, then limits. No filler; each sentence carries distinct information.

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 read-only tool with no output schema, the description covers purpose, the return shape, and the failure boundaries, which is nearly everything an agent needs. Remaining gap is precision on unit-code formatting and error behavior on mismatched dimensions.

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 67%; 'from' has an example hint while 'value' and 'to' are bare. The description's conversion examples (mi to km, GiB to GB, F to C) illustrate accepted unit-code format, but it doesn't clarify case-insensitivity, aliases, or whether value accepts negative numbers for temperature.

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 a number between units') and enumerates all supported dimensions, which immediately distinguishes it from generic siblings like calculate. An agent can tell what this does without opening the 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?

Gives positive guidance ('Use it when exact conversions matter') with examples, plus two explicit exclusions: no currency conversion and units must share a dimension. It doesn't name forex_market_hours as the alternative for currency, but the boundary is clear enough to route correctly.

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