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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open world), and the description adds genuinely useful context beyond them: a per-call price of 0.01 USDC on Base x402 and the X-Provider-Key header for customer-owned credentials. Cost and payment rail are exactly the kind of operational detail annotations cannot express. It stops short of saying whether the paid call is retried or refunded on failure.

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?

Two sentences, both load-bearing: the first gives the computation, inputs, and output unit; the second gives cost and credential mechanics. The core purpose is front-loaded and there is no filler or repetition of the name.

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 two-parameter pure-computation tool with full schema coverage and no output schema, this is nearly complete: the calculation, input meaning, output unit, price, and auth header are all stated. The only soft spot is that no return shape (bare number vs. object) is indicated, which matters slightly since no output schema exists.

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, and the description does add one real clarification by confirming the output is Celsius. However, the schema entries for both parameters defer back with 'see operation description for units and format,' and the description supplies only 'relative humidity' without a 0-100 range or a temperature scale note beyond the output unit, so it does not fully close that loop.

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 ('Calculate dew point'), states the output unit (Celsius), and even names the method (Magnus formula) plus the two required inputs. It is unambiguous, but it does not differentiate itself from the nearest sibling, api_weather_heat_index, which takes a similar temperature/humidity input shape.

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?

The inputs make the usage case obvious by implication (compute dew point from ambient temperature and relative humidity), but there is no explicit when-to-use or when-not guidance, and no routing to or away from api_weather_heat_index. A reader infers the case rather than being told it.

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