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

Goes well beyond the readOnlyHint/openWorldHint annotations: it discloses the data freshness limit ('end of day on the free plan'), the dual return format (USD per ounce plus the raw inverted rate), and the monetization model ($0.002 USDC per successful call via x402 on Base, Solana or Arc, with failed calls free). The 'failed calls are not charged' and settlement-chain details are exactly the kind of operational context an agent needs before invoking a paid call.

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-loads the resource and units, then freshness, then pricing — a sensible information order with no filler sentences. It loses a point because the embedded Chewy tracker pitch is irrelevant to this tool's purpose and dilutes an otherwise tight description.

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 does not need to enumerate return fields, and it covers everything else an agent needs: which metals, what unit, how stale the data can be, and what the call costs or doesn't cost. Nothing material is left ambiguous for a one-optional-parameter read tool.

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% and the single optional 'currencies' parameter already documents the allowed codes and the default of all four. The description restates the same four codes and adds only the unit framing (USD per troy ounce), which is useful but not parameter-specific meaning beyond the schema. 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?

Names a specific resource (latest precious-metal prices) and enumerates exactly which metals (XAU, XAG, XPD, XPT), the unit (USD per troy ounce), and the secondary outputs (raw ounce-per-USD rate, timestamp). It also explicitly excludes a misreading with 'Not a retail price list', so an agent can distinguish it from the commerce siblings without opening any schema.

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?

Provides a clear use context and an explicit exclusion ('Not a retail price list'), plus a pointer to a sibling 'for a different need'. The sibling it names (ecommerce_chewy_com) is a semantically unrelated cross-sell, so the routing guidance exists but is not a genuinely useful alternative for metal-price queries; there is no guidance on when spot vs. end-of-day data matters for choosing this tool.

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