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

Annotations already declare readOnlyHint and openWorldHint, but the description adds materially new behavior: a $0.01 USDC per-successful-call price on Base and a required x402-capable wallet client. Billing semantics ('per successful call') and the auth prerequisite are exactly the kind of context annotations 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 the capability before constraints and pricing; no filler. Slightly dense with mixed concerns (capability, restriction, price, auth) but each sentence earns its place.

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 usefully lists what comes back (issued time, temperature, winds, precipitation probability) and covers payment/auth constraints. It doesn't specify period granularity (hourly vs. daily) or response shape/pagination, leaving a small gap for a data-returning tool.

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 the baseline is 3, but the description clarifies the otherwise confusing maxItems parameter by tying it to 'forecast periods' (the schema text oddly mentions 'package tools cap release/dependency metadata'). It also reinforces the decimal coordinate format, adding modest value over the schema.

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+resource (read NWS land forecast periods) plus concrete scope (up to 14, decimal coordinates) and enumerates returned fields. It also draws a boundary against geocoding/address-lookup tools, which no sibling provides, so an agent can route correctly without opening the schema.

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 clear use conditions: only official NWS point and grid forecast URLs, no geocoding or address lookup, and requires an x402-capable wallet client. It doesn't name an alternative sibling tool for cases where the caller lacks a wallet or needs geocoding, so it stops short of full when/when-not/alternatives coverage.

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