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

Annotations already cover readOnly and open-world behavior, yet the description adds real value: the exact paid-call cost ($0.002 USDC via x402 on Base/Solana/Arc) and the fact failed calls are not charged. It also discloses upstream data-source limits (NOAA-only tides, no wind/pressure). It does not describe latency or rate limiting, keeping it from a 5.

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?

Three tight sentences: what is returned, what is excluded, then the pricing model. The primary capability is front-loaded and no sentence is filler.

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 an output schema present the description need not explain return shapes, and it still covers inputs, data-source constraints, and the payment mechanism. An agent has everything needed to decide and invoke correctly.

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 goes beyond the schema by explaining the conditional meaning of the optional 'station' parameter — supplying it is what triggers the tide-prediction branch of the response. Latitude/longitude semantics are left entirely to 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 pair: current wave height and period at a coordinate from Open-Meteo Marine, plus next-24h high/low tide predictions when a NOAA station id is supplied. That is precise enough to separate it from every sibling, none of which return marine or tide data.

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 scope conditions: tide predictions only exist for NOAA stations, and no wind or pressure forecast is included. It does not name an alternative tool or explicitly say when not to call it, so it stops short of a 5.

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