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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely useful behavior beyond that: the response embeds a melt calculation priced at the 'current website quote', so the agent knows the returned value is quote-dependent and time-sensitive rather than static. It stops short of covering not-found/error behavior.

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?

One dense sentence with no wasted words, but it is not front-loaded with an action verb, so the reader parses it as an entity definition before realizing it is a retrieval tool. Conciseness is fine; structure could be improved by leading with 'Retrieve a coin by ID...'.

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 annotations covering safety and an output schema covering the return shape, the description need not explain returned fields — though it partially does. The critical gap is the undocumented required `id` input and any failure mode, leaving an agent unable to confidently construct a call from the description alone.

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?

The schema has 0% description coverage on the single required `id` parameter, so the description carries the full burden and fails: it never mentions an identifier, what form it takes, or where to obtain it. It only weakly implies a single specific coin is returned.

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 is a noun phrase describing the resource ('A native precious-metal coin preset with issue years, image, specifications...') rather than a verb stating the operation, so the agent must infer that this retrieves a single coin. It does convey the resource scope (one coin, not a list), but it never distinguishes itself from siblings like find_coins or calculate_coin_value.

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?

There is no statement of when to use this tool versus find_coins (which presumably locates coins) or the calculate_* siblings. The mention of 'a quantity-one melt calculation' hints that a separate melt call may be unnecessary, but this is inference rather than guidance, and no prerequisites or exclusions are given.

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