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

Adds substantial context the annotations do not carry: a concrete price ($0.005/call), the USDC-on-Solana x402 payment mechanism, and the exact two-step protocol (call unpaid to receive the PaymentRequired challenge, retry with payment at _meta["x402/payment"]). That is genuinely actionable behavioral disclosure beyond readOnlyHint/openWorldHint.

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-loads what the tool does, then the source, then cost and payment mechanics, then an HTTP equivalent. Dense but every clause is functional; the payment sentence is long but necessary for a paid endpoint.

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 leaves the return payload entirely unspecified — an agent cannot tell whether it gets per-day temperatures, precipitation, wind, or units. Pricing and access are fully covered, but the shape of the result is not.

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 coverage is 100% with lat, lon, and days already documented (including "1-16, default 7"). The description restates the day range but adds no coordinate format, hemisphere/precision expectations, or units beyond the schema, so baseline 3 applies.

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?

"Daily forecast, 1-16 days" is a specific verb+resource with an explicit horizon, and it names the upstream source (Open-Meteo). It implicitly separates itself from weather_current and weather_alerts by saying "daily forecast" and stating a 1-16 day range, though neither sibling is named.

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 1-16 day scope implies when to reach for this rather than a current-conditions tool, but there is no explicit "use this instead of weather_current when..." routing. The only concrete guidance given is operational (the payment flow), not selection guidance.

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