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

Beyond the readOnly/openWorld annotations, the description discloses the response shape (timestamp, 24-hour change, market direction), the tier gating of custom currencies and history, and an explicit cost of 2 credits. That credit cost and plan gating are genuinely useful behavioral context an agent cannot get from annotations. It stops short of 5 because it never says what happens when a free-tier caller requests daily/hourly data.

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?

Two sentences, front-loaded with the core purpose and then the response/tier details. The only waste is the redundant 'Gold Price: Gold Price' opening that repeats the title verbatim.

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 values need not be explained, and the description still summarizes them usefully. With three all-optional parameters and a credit cost disclosed, an agent has enough to invoke it correctly; only the free-tier failure behavior of the gated flags is left unstated.

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 every parameter already carries a description, so the schema does the heavy lifting. The description adds that custom currencies and 7/30-day history are plan-gated, which implicitly explains why the currency, daily and hourly flags may fail or return nothing on a free plan — but it never ties that explicitly to the parameters.

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 ('fetches real-time spot gold prices') and pins down the units (troy ounce, gram, kilogram), which clearly separates it from metals siblings like SilverPrice, PlatinumPrice and PalladiumPrice. It does not explicitly name an alternative, so it stops short of a 5.

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?

Usage is implied by the resource itself — you call it when you want a current gold spot price — and the note about paid vs free plan features hints at tiering. However, there is no explicit statement of when to prefer this over CurrencyConverter, ExchangeRate or GlobalStockMarket, and no guidance on prerequisites for the paid-plan-only outputs.

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