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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so safety is covered. The description adds real context beyond them: the exact fields returned, the derivation rule that a PO amount comes from its lines, and the important caveat that unit_cost carries no currency so currency_code must be fetched separately.

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?

Three tight sentences with the returned fields front-loaded, then filters, then the currency caveat. Every sentence carries information; no filler or repetition.

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 compensates by naming the returned fields, and it flags the currency ambiguity an agent would otherwise get wrong. Pagination behavior is left to the schema, which documents it, so nothing critical is missing for a zero-required-parameter list tool.

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%, so page/per_page/part_id/purchase_order_id are already documented; baseline 3 applies. The description restates the two filter parameters without adding format, default, or pagination detail beyond what the schema 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?

State a specific verb and resource (list purchase order line items) and enumerates the returned fields (description, optional part, quantity, unit_cost, quantity_received) plus the filter keys. It is clearly distinguishable from list_purchase_orders and get_purchase_order_line by name and content, though it never names a sibling explicitly.

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 states which parameters filter the result (purchase_order_id or part_id) and adds a follow-up call instruction (get_organization_settings for currency_code), which is useful operating guidance. However, it never says when to prefer this over get_purchase_order_line or list_purchase_orders, leaving the choice to inference.

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