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

Annotations only say readOnly/openWorld; the description adds materially important behavior the agent cannot get elsewhere: a $0.002 USDC charge per successful call via x402 on Base/Solana/Arc, and that failed calls are not charged. Cost and payment-rail disclosure is high-value for an autonomous caller and is not inferable from the schema or annotations.

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?

Three tight sentences: identity first, disambiguation second, billing third. No filler, and the awkward 'route name is kept for the owner' note is a one-clause caveat rather than a distraction.

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 shape needn't be explained. The description still covers source, currency and unit, timestamp semantics, exclusions versus fixings/holdings, and the full payment model — everything needed to call this correctly and know what the caller is paying.

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 'metal' parameter already documents 'XAU (gold) or XAG (silver); default XAU'. The description repeats the same XAU/XAG framing without adding syntax or behavior beyond the schema, so the 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+resource with units and source: 'Live spot price of gold (XAU) or silver (XAG) in USD per troy ounce from gold-api.com.' It also pre-emptively distinguishes itself from LBMA London AM/PM fixing and vault holdings, which is exactly the confusion an agent would have with siblings like energy_lme_metal_cash_settled or energy_nickel_class1_cash_settle.

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 clear positive and negative selection criteria: this is a spot quote with a timestamp, not a fixing and not holdings. That tells the agent when this tool is the right one. It stops short of naming the alternative tool to call when a fixing or holdings data is actually wanted.

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