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

Annotations already cover the safety profile (read-only, non-destructive, closed world), so the bar is lower. The description adds genuinely useful behavior beyond them: the funding fee is rolled into the payment and no PMI is applied, and it lists the returned values (financed amount, payment, total interest), which matters since there is no output schema.

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 waste: the core behavior is front-loaded and the return values follow. Nothing is padded or 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 pure calculator with no output schema, the description is nearly sufficient: it names the output fields and the funding-fee/no-PMI behavior. It leaves minor gaps such as the default fee handling and output units, but nothing that would cause a mis-invocation.

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 all four parameters (apr, fee, term, principal) are already documented in the schema. The description restates that a funding fee is included but adds no units, ranges, or formatting guidance beyond what the schema provides.

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 specific verb (calculate) and resource (monthly VA loan payment), plus the defining traits that separate it from a generic mortgage: it includes the funding fee and has no PMI. It does not name the obvious sibling mortgage_payment, so the agent must infer the distinction from the VA-specific framing.

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?

The VA/funding-fee/no-PMI framing implies when this tool applies, but the description never states when to choose it over mortgage_payment or auto_loan. Usage is implied rather than directed, with no exclusions or alternatives named.

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