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

Annotations already declare this read-only, idempotent and non-destructive, and the description is consistent with that. It adds the genuinely non-obvious behavior: the call is paid ($0.01 USDC via x402), which is not derivable from annotations and matters for agent decision-making; it stops short of restating the 402 retry flow, which the schema covers.

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?

A single sentence front-loads purpose, provider and price with zero filler. Nothing is repeated from the schema or annotations beyond the implicit field name.

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 simple two-parameter read tool whose schema fully documents the payment flow, the description covers purpose, source and cost. It omits response shape (units, fields returned) and there is no output schema, but that gap is minor for a well-known weather payload.

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%, so both parameters are fully documented in structured fields. The description only implies that 'city' drives the query and adds no format, casing or payment semantics beyond it; 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?

States a specific verb and resource ('Live current weather for any city'), names the upstream provider (Open-Meteo), and gives the concrete endpoint path. No sibling tool overlaps with weather, so an agent can select it unambiguously at a glance.

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?

Usage is only implied: you call it to get weather for a city. It doesn't say when to prefer it (e.g. 'live' vs. any forecast alternative) or hint that a first call without payment returns a 402 challenge — that guidance lives in the schema, not the description.

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