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

Annotations declare a mutating, non-idempotent, destructive write, and the description adds context those flags cannot convey: the sealed-invoice gate and the required add_line suggestion workflow. It does not explain why the operation is flagged destructive or whether duplicate calls create duplicate lines, so it stops short of exhaustive.

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 tight sentences with no filler; the field list is front-loaded and the sealing caveat is placed second, which matches its conditional nature. Nothing is wasted or buried.

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 an output schema present there is no need to describe returns, and the description covers the mutation's key constraint and the unusual 'minor units' rate convention. Minor gaps remain around invoiceId semantics and quantity/rate limits, but nothing essential to calling the tool 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 0%, so the description carries the burden. It adds real meaning for rateMinor ('whole minor units') and lists the unit enum, but the other fields are mostly name restatements, and invoiceId plus the quantity/rate bounds are never addressed.

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?

States a concrete verb and resource ('Add one line') and immediately enumerates the fields the line carries, so the agent knows this creates a line item rather than quoting a rate (quote_line_rate) or mutating an existing line (set_line_quantity). The mention of sealing ties it unambiguously to invoices.

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?

Gives an explicit when-not condition: once the invoice is sealed a new line is refused until accept_invoice_change applies an add_line suggestion, naming the alternative pathway. The positive when-to-use case (adding a line to an open invoice) is implied rather than stated, which keeps it 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.