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

Annotations already establish the safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint). The description adds genuinely new behavioral context not present in annotations: the output cadence (hourly then 6-hourly), the ~9 day horizon, and the x402 pricing model with a free daily allowance followed by per-call charges.

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?

Two compact clauses with zero filler, and the substantive content (granularity, horizon, variables) is front-loaded ahead of the billing note.

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?

An output schema exists, so return-value explanation is not required, and the description covers cadence, horizon, variables, and cost. Minor gaps remain around coordinate formatting and timezone/units, but for a two-parameter lookup tool this is close to complete.

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 are already documented in the schema and the baseline is 3. The description adds nothing about coordinate format, precision, or units beyond what the schema provides.

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?

The description names a specific resource (weather forecast) and scopes it precisely: hourly-then-6-hourly granularity, ~9 days, and the variables returned (temperature, wind, cloud, precipitation, symbol). It does not, however, differentiate itself from the obvious sibling global-weather__forecast-complete or us-weather__forecast, leaving the agent to infer the boundary.

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?

There is no guidance on when to choose this tool over global-weather__forecast-complete or the us-weather forecast variants. The only conditional content is billing ('free within the daily allowance, then $0.002 USDC per call'), which is cost information rather than usage guidance.

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