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

Annotations already declare readOnlyHint, openWorldHint, and destructiveHint=false, so safety is covered. The description adds genuinely useful behavioral context beyond them: the 2-credit cost and the fact that currencies beyond USD, highs/lows, changes, and history are gated behind paid plans, which affects whether a request will return the expected 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 tight sentences: the first front-loads what the tool returns, the second covers plan-gated extras and cost. No filler or repetition, and the parenthetical cost note is compact.

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, return values need not be described, and the description covers data scope, tier gating, and cost well. It does not state what the free tier actually returns when a paid-only field is requested (error vs. omission), which matters for correct invocation.

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%, so all three parameters are already documented, establishing a baseline of 3. The description exceeds that by revealing that the currency option is effectively limited on free plans (172 currencies on paid), which is meaning the schema does not convey.

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?

The description states a specific resource and scope: spot silver prices per troy ounce, gram, and kilogram in USD, plus 24h change and trend. It is immediately distinguishable from GoldPrice/PlatinumPrice by the metal, though no sibling is named explicitly.

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?

The plan-tier sentence implies when richer data (non-USD currencies, history, 30-day stats) is available versus the free spot quote, which is useful implied guidance. However, there is no explicit when-to-use/when-not guidance against alternatives such as CurrencyRate or GoldPrice for cross-asset comparisons.

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