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

Annotations already cover read-only, idempotent and non-destructive behavior, so the description is free to add return-shape context: it discloses that line items are expanded inline along with supplier, dates and status. It doesn't state what happens for a missing ID, but the expansion behavior is genuinely useful information not available elsewhere.

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?

One compact sentence with no filler, front-loading the resource ('One purchase order') before the contents. It is arguably too terse to be maximally useful, but nothing is wasted.

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?

For a simple single-record read with full annotation coverage, the essential facts are present. With no output schema, however, the description only gestures at the response ('dates') and says nothing about not-found behavior or the shape of the returned line items.

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?

There is a single required parameter with 100% schema description coverage, including the instruction to source it from list_purchase_orders. The description adds nothing about the ID's type or origin, 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?

The sentence names a specific resource ('One purchase order') and enumerates what it includes (supplier, dates, status, line items), which distinguishes it from the sibling list_purchase_orders by scope. There is no explicit verb, but 'One purchase order ... and its line items' clearly implies a single-record retrieval.

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 gives no when-to-use guidance and never names list_purchase_orders as the alternative for browsing or finding an ID. The only routing hint ('purchase_order_id from list_purchase_orders') lives in the schema, not the description.

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