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

Annotations already declare destructiveHint=true, readOnlyHint=false, idempotentHint=false and openWorldHint=false, so the safety profile is covered. The description adds a genuine behavioral trait beyond that: the post-seal refusal rule and the accept_invoice_change escape hatch, which is exactly the kind of lifecycle constraint an agent cannot get from annotations.

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, with the value-format constraint front-loaded and the lifecycle caveat second. Every clause adds either a format rule or a usage constraint.

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 described, and annotations cover the mutation safety profile. What remains thin is what happens to the previously stored date and what error surfaces on refusal, but the seal constraint covers the main operational risk for a 2-param mutation.

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 must carry parameter meaning. It restates the dueOn format already enforced by the schema pattern and says nothing about invoiceId beyond its name, leaving the coverage gap only partly filled; 'invoiceId' as a UUID reference is largely self-evident, so this is adequate rather than rich.

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 names a specific verb and resource ('Set the due date') and constrains the value form, so the operation is unambiguous. It also names a sibling (accept_invoice_change) in the sealed-invoice case, which helps distinguish the tool's role, though it doesn't contrast against suggest_invoice_change directly.

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 an explicit when-not rule: after the invoice is sealed, a different date is refused until accept_invoice_change applies a move_due_date suggestion, which effectively routes the agent to the alternative. It stops short of stating general prerequisites (e.g., must the invoice exist in a draft state, permissions required).

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