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

Annotations already declare read-only, idempotent, non-destructive behavior, so the safety profile is covered. The description earns credit by adding a real behavioral trait not in the schema: unit_cost is a bare number lacking currency, and currency_code must be fetched from get_organization_settings before stating a monetary value.

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 followed immediately by the one non-obvious caveat. No filler.

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's note about the bare unit_cost number and the required currency lookup covers the highest-risk ambiguity for a caller. It is nearly complete, missing only explicit sibling routing.

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 100% and there is exactly one parameter (id), which the schema fully documents. The description says nothing additional about the id parameter; the unit_cost note concerns a return field, not a parameter, so baseline 3 applies.

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 ('Get one purchase order line item by ID'), and 'one ... by ID' implicitly distinguishes it from list_purchase_order_lines and get_purchase_order. It's clear, though it never names or explicitly contrasts with those siblings.

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 guidance on when to use this versus list_purchase_order_lines or get_purchase_order. The only procedural hint is the downstream call to get_organization_settings, which is field-handling advice rather than when-to-use/routing guidance.

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