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

With no annotations, the description carries the full burden and does well: it discloses the pricing model ($0.01 for hours ≤ 48, $0.03 beyond), the HTTP GET endpoint, the data provenance (NWS-derived, bias-blended with a calibrated station model), and that every response labels the producing method. It omits auth/payment mechanics beyond 'x402' and does not describe the return payload's structure or error behavior.

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?

The core purpose and constraints are front-loaded, and the bracketed metadata block efficiently carries endpoint, pricing, and docs. There is mild redundancy between the first two sentences, which both restate 'hourly Washington, DC weather forecast', but overall it is tight and well ordered.

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 forecast tool with no output schema, the description covers provenance, pricing, chaining relationship to the point endpoint, and documentation. The gaps are the undocumented 'units' parameter and the 168-vs-240-hour discrepancy, which could cause an agent to under-request the available horizon.

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 0%, so the description must compensate for two documented-in-schema-only parameters — and it only partially does. It references a horizon limit ('up to 168 hours out') that conflicts with the schema's maximum of 240, and it never mentions the 'units' enum at all, leaving the agent to infer metric/imperial semantics from the schema alone.

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 resource (hourly Washington, DC weather forecast), the variables returned (temperature, precipitation probability, wind), and the horizon (up to 168 hours). It explicitly positions itself against the sibling endpoint by noting it is the same shape as /v1/forecast/point with DC coordinates built in, so an agent can distinguish it from weather_forecast-point and the other city variants.

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 description gives clear context for when this applies: hourly forecast for Washington, DC specifically, with the fixed-coordinate convenience versus the generic point endpoint. It does not state when NOT to use it (e.g. that weather_forecast-window_washington-dc or weather_forecast-probabilistic exist for different needs), so it stops short of explicit routing.

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