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

Annotations already establish read-only, idempotent, non-destructive behavior. Beyond that, the description adds genuine behavioral context an agent would otherwise lack: prices are VAT inclusive, denominated in euro per gram or per piece, include a spot quote time for spot-linked products, and indicate stock status. Only missing is any note on caching/refresh cadence for the 'today' pricing.

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 dense sentences that front-load the value proposition and then the calling convention, with no filler. The first sentence is long and carries several read-only facts at once, but every clause earns its place.

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 no output schema, the description carries the burden of describing returns and does so: currency, per-gram vs per-piece units, VAT inclusion, spot quote time, and in-stock status. Combined with the parameter guidance and the website parity note, an agent has everything needed to call and interpret the result.

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 the single parameter is fully documented with examples in the schema itself, so the baseline is 3. The description restates the same slug-or-name and omit-for-all semantics, adding no new syntax or format detail beyond what the schema already provides.

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 gives a specific verb-and-resource statement: what Liffey Metals 'charges today' for casting grain, coins and bars, with currency and unit of measure. It implicitly separates itself from get_buy_price by framing the figures as what the vendor charges rather than pays, but it never names that sibling, so an agent must infer the distinction.

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?

It clearly explains the filtering dimension ('give a product slug ... for one product; omit for every product'), which tells the agent how to call it in both the filtered and unfiltered modes. However, it gives no guidance on when to choose this over the closely named sibling get_buy_price or get_buy_prices, leaving the most error-prone routing decision implied.

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