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

Annotations already declare readOnly/idempotent/open-world, and the description adds material behavior beyond them: the paid x402 USDC-on-Base pricing model, the exact $0.002 cost, that failed/out-of-US calls are not charged, and that a payment-less call returns a PaymentRequired object. That is context an agent cannot get from the annotations or schema.

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 use case, then output shape, then constraints and pricing — a sensible order with no filler sentences. It is a single dense paragraph, though, and the return-value inventory could be tightened.

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?

There is no output schema, yet the description enumerates the returned fields (name, °F/°C temperature, wind, precipitation chance, short/detailed forecast, nearest city/state, time zone, forecast zone, alerts summary), covers error behavior, cost, and the hourly alternative. Nothing an agent needs to call or interpret this tool 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 description coverage is 100%, so the baseline is 3, but the description adds real semantics: the hourly=true branch caps at 48 periods (matching the 'hours' param), alerts=false suppresses the alert lookup, and lat/lon versus place are presented as alternatives. It stops short of detailing units or precedence between lat/lon and place.

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 pair (resolves lat/lon or US place to an NWS grid and returns a 7-day forecast) and explicitly scopes itself as the US/official-NWS option, distinguishing it from the global 'weather' sibling. An agent can identify both what it does and what it does not cover 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?

Names concrete use cases (trip, event, delivery, field-work planning) and the selecting condition ('when an official forecast matters'), then names the alternative for out-of-scope calls: points outside the US return 404 and should use /v1/weather (MET Norway). Both when-to-use and when-not-to-use are covered.

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