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

Annotations already declare readOnlyHint=true, idempotentHint=true, and openWorldHint=false, so the safety profile is covered for this pure computation. The description adds an output-flavored example ('saves $64,927 and 5½ years'), hinting at what results look like. It does not describe the result structure or payoff-date output beyond that teaser.

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?

Front-loads a concrete worked example, then states the modeling capability in one sentence, then a reference URL. Two sentences carry the load with little waste, though the trailing URL adds marginal value.

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 10-parameter, all-optional tool with no output schema, the description gives a helpful example of the payoff outcome but never explains the returned fields (e.g., payoff date, total interest saved). Annotations cover the safety side, but the return-value context is left thin for a tool without an output schema.

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 ten parameters (extra, lump, biweekly, rate, etc.) are already documented in the schema. The description only names the same concepts (extra payments, lump sum, biweekly) with no added syntax, units, or interaction detail. Baseline 3 applies when the schema does the heavy lifting.

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 clear verb+resource: 'Model extra payments, a lump sum or biweekly in this mortgage payoff calculator.' The extra-payment/lump-sum/biweekly focus distinguishes it from generic siblings like mortgage_calculator and amortization_calculator without naming them explicitly. An agent can pick it out for payoff-with-extra-payments scenarios.

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 description implies usage by saying it models extra payments, a lump sum, or biweekly payments, which signals the scenario it fits. However, it never explicitly says when to use it versus mortgage_calculator, amortization_calculator, or credit_card_payoff_calculator, nor any exclusions. Usage is inferred rather than stated.

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