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

Goes well beyond the readOnlyHint/openWorldHint annotations: it names the upstream source (FRED, World Bank), the currency (USD), the cadence (monthly), the history ceiling (24 months), and the billing model ($0.002 USDC per successful call via x402 on Base, Solana or Arc, failures not charged). The payment disclosure is exactly the kind of behavioral fact an agent must know before invoking.

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 what the data is, followed by the naming caveat, the coverage window, and the price. Every sentence carries information an agent needs; nothing is padded.

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?

Return values are covered by the output schema and the billing/source context is thorough. The one residual gap is the schema's odd string typing for months, which the description does not flag, leaving a minor risk of a wrong argument type.

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 the months parameter (1–24, default 3) is already documented. The description only corroborates it with 'Latest value plus up to 24 months of history', adding the small nuance that the latest point is always returned regardless of window; that is marginal value over the schema, so 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: monthly copper, aluminium and zinc reference prices from FRED/World Bank in USD. It also explicitly distinguishes itself from LME cash-settlement pricing and from the route name, so an agent can tell it apart from siblings such as energy_nickel_class1_cash_settle or energy_precious_metals_spot_fix.

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?

Clear usage context: World Bank reference series rather than LME settlement, monthly frequency, latest value plus up to 24 months of history. It does not name a specific alternative for LME-style settlement data or state exclusions, so it stops short of explicit when/when-not routing.

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