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

Annotations already declare destructiveHint=true, idempotentHint=false, and readOnlyHint=false, so the safety profile is covered. The description adds genuinely new behavioral context beyond that: the sealed-invoice refusal rule and the required remediation flow through accept_invoice_change, which an agent could not infer from the annotations alone.

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, zero filler, and the core action is front-loaded ahead of the constraint. Every clause earns its place by conveying either the operation or a non-obvious workflow rule.

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?

An output schema exists, so return values need not be explained, and the sealed-invoice workflow rule is a valuable addition. However, with zero parameter documentation and no mention of auth or the effect on existing line totals, the definition is only minimally complete for a destructive mutation 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 0%, so the description carries the full burden for three required parameters, yet it only implies that 'one line' is identified by an id. It says nothing about invoiceId being a UUID, the 1-10000 quantity bounds, or whether quantity is absolute versus relative.

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 gives a specific verb and resource: 'Set the quantity on one line.' It is unambiguous about what is mutated, though it does not distinguish itself from sibling tools like place_line or offer_discount beyond the resource it touches.

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 the key usage constraint explicitly: after the invoice is sealed, a different quantity is refused, and it names the correct alternative path (accept_invoice_change applying an adjust_quantity suggestion). That is a clear when-not plus alternative, though it omits other preconditions such as required permissions or draft-state expectations.

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