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

Annotations already declare readOnly/idempotent/non-destructive/closed-world. Beyond that, the description adds a genuinely useful computational convention ('interest is rounded to the cent each month') and discloses the two output modes, which is real behavioral context not present in structured fields.

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?

Three tight sentences with no filler; the identity/rounding statement is front-loaded and the include_schedule branch follows logically. Nothing wasted, nothing padded.

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 read-only calculator with no output schema, the description names the returned aggregate fields (payment, payoff date, total interest, total paid) and the schedule mode, which is what an agent needs. The gaps are the undocumented numeric parameters, particularly extraMonthly's behavior.

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 only 17% (one of six params documented), so the description must compensate. It explains include_schedule's branching semantics well but says nothing about extraMonthly (does it shorten term or lower payment?) or firstPaymentDate's effect on the schedule start.

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 and resource: it produces a 'fully amortizing mortgage schedule' with interest rounded monthly. An agent can distinguish it from the other calculate_* siblings (dscr, cap_rate, cash_flow) on domain alone, though the description never explicitly contrasts itself with them.

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 implied by the domain (compute a mortgage amortization schedule) rather than stated. There is no explicit when-not-to-use or named alternative, though the sibling set is functionally distinct so mis-selection risk is low.

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