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

Annotations already declare readOnlyHint, openWorldHint and idempotentHint, so the safety profile is covered. The description adds valuable context the annotations do not: the $0.006 per-call price on USDC/Base via x402 and the payment-requirements-returned behavior when no signature is supplied. It does not describe rate limits or response shape, but the payment flow disclosure is a meaningful addition.

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 description is compact and front-loaded, leading with what the tool returns before giving usage context, price and sample path. Sentences are efficient, though the pricing/payment sentence is fairly dense with x402 jargon.

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 weather lookup, the description covers purpose, use cases, cost, and the payment handshake, which is what an agent needs to invoke it correctly. The lack of any note on return format (current vs. daily fields) is a minor gap given no output schema exists, but the payment flow is fully explained.

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 all six parameters are already well documented in the schema (lat/lon alternatives, days range 1-9, country disambiguation, payment_signature semantics). The description adds no parameter detail beyond the schema, so the baseline of 3 is appropriate.

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: 'Get current weather and a 7-day forecast for any city or coordinate.' This is much more specific than a tautology and covers the data provided. It does not, however, distinguish itself from the sibling airport_weather tool, leaving ambiguity about which weather tool to pick.

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?

Provides clear situational guidance: 'before travel, logistics, events or field work' and 'Use when a plan depends on the weather in the coming days.' This gives concrete context for when to reach for it, though it offers no explicit alternatives or when-not-to-use conditions relative to the sibling weather tool.

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