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

The description adds meaningful behavior beyond the annotations: the required purchase_orders:write scope, the inventory side effect (quantity changes propagate to the part's stock), and the immutability rule that a line with received stock cannot change its part. The annotations only supply the generic destructive/idempotent profile, so this extra context is genuinely additive.

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 core action first, then the auth requirement, then the two operational rules. Every sentence carries information and nothing is repeated.

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 7-parameter mutation tool with no output schema, the description covers authorization, side effects, and a key business constraint. It could still say more about what the response returns or what happens to line fields after partial receipt, but nothing needed to invoke it correctly is missing.

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 the baseline is 3, but the description goes further by explaining the intended use of quantity_received (goods receipt) and the interaction between part_id and already-received stock. That adds semantics the schema's terse 'Part from inventory' text does not convey.

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 opens with a specific verb+resource ('Update a purchase order line item'), which cleanly separates it from create_purchase_order_line, delete_purchase_order_line, and list_purchase_order_lines. It does not differentiate itself from the other update_* siblings in the family, but the resource is unambiguous.

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 gives one concrete usage recipe ('To receive goods, set quantity_received'), which is a real when-to-use cue. However it never says when to prefer this over bulk_update or update_purchase_order, and no exclusions or prerequisites beyond the scope string are stated, so guidance is implied rather than explicit.

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