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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so safety is covered. The description adds that early-payment discount dates are also produced, which is useful behavior beyond the annotations, but it says nothing about what happens with unrecognized or malformed terms, nor whether a discount term like '2/10 net 30' yields multiple computed dates.

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?

A single front-loaded sentence: purpose first, then the parenthetical of supported formats, then the discount-date caveat. No filler, no repetition of the title, and no restatement of schema fields.

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 two-parameter pure calculation this is mostly sufficient, and the supported-term list removes the main ambiguity. However, with no output schema present, the description never says what is returned (a single YYYY-MM-DD string? a separate discount date field?), which leaves an agent guessing at the response shape for the '2/10 net 30' cases it advertises.

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 coverage is 100%, so the baseline is 3, but the description genuinely extends the 'terms' parameter by listing accepted forms ('net 30', 'due on receipt', 'EOM', 'net 30 EOM', '2/10 net 30') that the schema only gestures at with 'e.g. "net 30"'. That enumeration is real added meaning an agent would otherwise have to guess at.

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 pair ('Exact due date for an invoice') and enumerates the term formats it understands, so an agent can immediately tell this is a payment-terms date calculator rather than a lateness or fee tool. It stops short of naming a sibling such as how_late_is_this_invoice or late_fee_calculator to draw the boundary explicitly.

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?

Usage is only implied by the calculation framing: an agent can infer this is the tool to call when it has an invoice date and terms and needs the due date. There is no explicit when-to-use vs. when-not guidance, nor any statement that lateness or fee calculation belongs to the sibling tools.

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