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

Annotations are absent, so the description carries full burden. It discloses that currencies not listed in `prices` are converted from the base price at invoice time, a key behavioral detail. However, it does not mention the return value or that this is a persistent (reusable) object beyond 'reusable', nor any error conditions.

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 with no fluff; the key decision (use `prices` vs conversion) is front-loaded. It omits unnecessary details, though it could be more concise by dropping the parenthetical example, but overall well-paced.

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 7 parameters and no output schema, the description covers the trickiest part (currency handling) and leaves parameter details to the schema, which is rich (86% coverage). It's complete enough for an agent to call the tool correctly, though it could mention idempotency or reuse semantics.

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 86%, and the schema already explains most parameters. The description adds clarity on the relationship between `unitPrice`, `baseCurrency`, and `prices`, which the schema lacks, but does not cover all nuances like the decimal-place rule for JPY (only in schema). Thus, a baseline 3 with marginal added value is appropriate.

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 opens with a specific verb and resource ('Create a reusable invoice item'), which clearly distinguishes it from its sibling list/update counterparts. It also explains the item's reusability, adding domain context beyond the name.

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 description explains when to use `prices` versus relying on `unitPrice` and base currency conversion, giving direct guidance on a key decision. It does not explicitly state when not to use this tool versus alternatives, but the sibling context makes the create-only purpose clear.

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