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

Annotations already cover the read-only/idempotent/open-world safety profile, and the description adds what they cannot: a $0.01 USDC per-successful-call x402 payment on Solana, the coverage boundary, and an equivalent HTTPS GET endpoint for non-MCP callers. Cost and payment requirements are exactly the pre-invocation facts an agent needs.

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 what the tool returns, then scope, then price and transport. Every sentence carries information an agent needs before calling; no filler.

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?

With no output schema, the description still enumerates the returned fields (temperature, precipitation chance, wind, text forecast, alerts), the two forecast modes, unit behavior, geographic limits, and the payment model. Nothing material is missing for correct invocation.

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 lat/lon/units/hourly are already fully documented and the baseline is 3. The description adds only the framing that hourly yields 48 periods instead of 14 day/night periods, which the schema already states almost verbatim.

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 (US NWS forecast for a lat/lon point) plus exactly what it returns: 7-day or hourly periods with temperature, precipitation, wind, text, and active watches/warnings/advisories. It also distinguishes itself from the sibling weather_global by declaring the US-states/territories/coastal-waters-only scope.

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 a clear use condition (US coordinates only) and an explicit exclusion (outside US/territories/coastal waters), plus the hourly-vs-daily switch and the HTTPS alternative endpoint. It never names weather_global as the fallback for non-US points, so the alternative is only implied by the geographic exclusion.

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