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

The annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description is not asked to carry that burden. It does add non-obvious behavioral context: unit_cost is a bare number with no currency, plus the follow-up call needed to interpret it. It doesn't describe return shape or error behavior, so not a 5.

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, no filler: the retrieval purpose leads and the unit_cost/currency caveat follows. Every sentence earns its place.

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-entity getter with no output schema, the description covers the one genuinely surprising detail (currency-less unit_cost) and how to resolve it. It leaves general return-field composition unaddressed, but that gap is minor given the tool's simplicity.

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 'id' parameter at 100% schema description coverage, so the schema fully documents the input. The description adds no format or sourcing detail for the ID beyond what the schema already gives, so the 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 description states a specific verb ('Get') plus resource ('purchase order line item') and qualifies it with 'one ... by ID', which cleanly separates this single-fetch tool from the sibling list_purchase_order_lines. An agent can pick it without inspecting the 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?

It establishes the when: fetching a single line by ID, and adds a concrete cross-tool instruction (call get_organization_settings for currency_code before stating a currency). It doesn't name the list/update siblings or any exclusions, so it stops short of a 5.

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