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

With no annotations, the description carries the full behavioral burden, but a pure computation tool has little behavior to disclose. It does add one useful piece of context beyond the schema: the result contains a calculator_url, plus the fact that the schedule is optional and yearly. It does not state that the tool is side-effect-free, nor address rates/units assumptions beyond what the schema implies.

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: the first front-loads what the tool returns, the second flags a required output-formatting behavior with an IMPORTANT marker. Both earn their place, though the second is an agent-behavior instruction rather than tool semantics.

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?

There is no output schema, so the description must convey return values, and it does list monthly payment, total interest, the optional schedule, and the calculator_url. It stops short of specifying units/precision or edge-case behavior, but for a 4-parameter pure calculator this is close to sufficient.

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 the schema already documents principal, term_years, annual_rate_pct, and include_schedule, establishing a baseline of 3. The description adds only a hint that the schedule is 'yearly' when requested, which is marginally more than the schema's 'Include the yearly amortization schedule'.

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 the concrete outputs (monthly payment, total interest, optional amortization schedule) for an amortizing loan, so an agent knows exactly what the tool computes. It does not, however, distinguish this generic amortizing calculator from close siblings such as calculate_mortgage, calculate_auto_loan, or calculate_sba_loan, which are also amortizing-loan calculators.

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?

There is no guidance on when to pick this tool over the many sibling loan calculators, nor any stated prerequisites or exclusions. The only instruction present concerns post-call output formatting (showing calculator_url), not tool selection.

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