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

Annotations cover the read-only/open-world profile, and the description adds highly consequential context they cannot: the $0.002 USDC per-successful-call cost, the x402 payment rails (Base, Solana, Arc) and that failed calls are not charged. Cost and payment mechanics are precisely what an agent needs before invoking a paid tool.

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 lead sentence carries the identity and units, and the pricing note is placed last where it belongs. The clause 'the route name is kept for the owner' is minor internal noise that does not help an agent decide anything.

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, return values need no prose, and the description still supplies series ID, units, cadence, history depth, cost and payment rails. Nothing needed to call it correctly is missing.

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 reinforces the ceiling ('up to 24 months of history') and clarifies the result shape ('latest value plus up to 24 months'), which adds meaning about what the months parameter actually controls.

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 (Australian thermal coal reference price), unit (USD per metric ton), cadence (monthly) and exact source (World Bank PCOALAUUSDM via FRED). It also explicitly disambiguates from the Newcastle FOB spot index and Richards Bay, which is exactly the confusion the route name invites.

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?

The exclusions ('Not the Newcastle FOB spot index or Richards Bay prices') route the agent away from mismatched expectations, but there is no positive statement of when to pick this over adjacent price series. It is a clear context statement rather than a full when/when-not rule set.

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