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

Goes well beyond readOnlyHint/openWorldHint by disclosing the upstream source and series ID, the returned history depth, and a concrete payment model ($0.002 USDC per successful call via x402 on Base/Solana/Arc, failures not charged). Return shape is left to the output schema, which is acceptable here.

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?

Front-loaded with the price definition, then exclusions, then payload/pricing facts; each sentence carries information. The clause about the route name being kept for the owner is marginally useful context rather than noise.

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?

For a single-optional-parameter read tool with annotations and an output schema, the description supplies source, units, history depth, cost, and disambiguation – everything an agent needs to call it 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% and already documents 'months' with range and default. The description adds only a light clarification ('Latest value plus up to 24 months of history'), so the baseline 3 applies – it does not explain units of history or how the latest value relates to the months count.

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 and scope: 'Monthly nickel reference price in USD per metric ton (World Bank series PNICKUSDM, via FRED)'. It also pre-empts the most likely confusion by naming the sibling product (LME Class 1 cash settlement / warehouse stocks) that this is NOT.

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?

Explicitly excludes the LME cash-settlement interpretation, which routes the agent to energy_lme_metal_cash_settled for that need. There is no positive 'use this when...' statement, but the exclusion plus source naming gives strong selection context.

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