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

With annotations only declaring readOnlyHint and openWorldHint, the description carries the essential behavioral facts: the call costs $0.02 USDC, an unpaid call returns x402 payment requirements rather than data, and the retry path is via X-PAYMENT or PAYMENT-SIGNATURE headers. That is precisely the kind of operational context structured fields cannot express.

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?

Four short sentences, front-loaded with what the tool returns, then coverage, cost, and the failure/retry path. The Open-Meteo aside is mildly tangential but explains a sourcing choice an agent might otherwise question.

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 read-only, two-parameter tool with no output schema, the description covers cost, payment failure mode, retry mechanism, and geographic scope. It stops short of saying what a 'forecast period' contains (hourly vs daily, count of periods), which is the main remaining gap given there is no output schema.

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; saying 'CONUS coordinates' maps to the latitude/longitude bounds in the schema and is genuinely useful. It also reveals a payment channel parameter (params._meta["x402/payment"]) absent from the schema, though it never states that coordinates are decimal degrees or how the values map to the min/max ranges.

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 (NWS forecast periods) and scopes it to CONUS coordinates, so an agent knows what it returns. It does not distinguish itself from the closest sibling, place_weather_alerts, which also covers US weather data, so the boundary between forecasts and alerts is left to inference.

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?

It gives a clear geographic inclusion rule (CONUS coordinates), states that an alternative data source is intentionally excluded, and explains the paid-call workflow. It never says when to prefer place_weather_alerts instead, so routing among weather siblings is incomplete.

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