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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds genuine business context beyond that: the relationship 'a PO with lines takes its amount from them' and the warning that unit_cost carries no currency, directing the agent to get_organization_settings for currency_code.

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?

Four tight sentences, front-loaded with the purpose and followed by the fields, filters, and the currency caveat. Each sentence carries distinct information, though the currency instruction is slightly dense compared to the rest.

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 usefully enumerates the returned fields and discloses the currency-format caveat and the PO-amount rule. Pagination behavior is left to the schema, which documents auto-fetching, so the definition is essentially complete for an agent to call it correctly.

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 page, per_page, part_id and purchase_order_id are already fully documented. The description reiterates the filter parameters but adds no format or semantics beyond the schema (the unit_cost note concerns returned data, not inputs), so the baseline 3 holds.

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 ('List') and resource ('purchase order line items'), then enumerates the returned fields (description, optional part, quantity, unit_cost, quantity_received). This distinguishes it from the sibling list_purchase_orders and get_purchase_order_line without opening a schema.

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?

'Filter by purchase_order_id or part_id' implies the two usage contexts (lines for a PO, or lines for a part), and the currency note gives downstream guidance. However, it never explicitly states when to use this versus get_purchase_order_line or list_purchase_orders, and gives no exclusions, so usage is only implied.

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