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

Beyond the readOnlyHint annotation, it discloses that premium_over_spot_bps is nullable and why (null when live reference inputs are unavailable), names the error code returned for unsupported countries, states the plan/auth requirement, and points to static sample responses for evaluation. That is substantial behavioral context an agent cannot get from annotations alone.

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?

Purpose is front-loaded in the opening clause, and the trailing clauses each carry distinct information (nullability, code format, error behavior, plan gating, docs link). It is dense — one long sentence with several embedded clauses — but no sentence is padding.

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?

An output schema exists, so return structure need not be restated; the description still clarifies the one non-obvious output field's null semantics. With the single parameter fully explained, the error path and auth requirement covered, and docs linked, nothing needed to call this 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 description coverage is 0%, so the description must carry the parameter burden, and it does: it specifies that country is an ISO 3166-1 alpha-2 code and supplies concrete examples (ID, MY, AE, JP), plus the behavior for uncovered values. It fully compensates for the empty schema documentation.

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: 'Return the latest per-country physical dealer/retail gold prices.' It explicitly distinguishes itself from the spot tool by asserting the quotes are 'real quotes from dealers, mints, and bullion benchmarks, NOT spot-derived arithmetic,' so an agent can separate it from the get_spot_price sibling.

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 real selection context: uncovered countries return unknown_country and the endpoint requires Basic or higher, which tells the agent when the call will fail. The contrast with spot-derived pricing implies the alternative tool, but it never names get_spot_price directly or states the explicit condition for choosing between them.

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