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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the agent knows this is a safe read operation. The description adds meaningful behavioral context: break-even analysis, monthly savings, and the warning about term reset making a lower payment cost more overall. This goes beyond the annotation baseline.

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?

The description is two sentences, front-loaded with the main question ('Whether refinancing is worth it') and then adds a valuable nuance about lifetime interest. Every sentence earns its place with no fluff or repetition.

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?

With no output schema, the description explains all key outputs (new payment, monthly saving, break-even months, lifetime interest) and the decision context. Optional parameters like financeClosingCosts and newTermYears are not mentioned explicitly, but the schema covers them. The description is complete enough for a calculator tool.

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% with descriptions for all 7 parameters, so the baseline is 3. The tool description does not add additional parameter-level semantics beyond the schema; it only mentions 'closing costs' and 'term reset' in a general sense, which does not exceed what the schema already 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?

The description clearly states that the tool evaluates whether refinancing is worth it, listing specific outputs: new payment, monthly savings, break-even months, and lifetime interest comparison. It distinguishes from sibling tools like calculate_mortgage and compare_loans by focusing specifically on refinance decisions.

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 context (when considering refinancing) and highlights the lifetime interest comparison as a key differentiator that catches a common trap. It does not explicitly name alternative tools or state when not to use, but the context is clear enough for an AI agent to select it correctly.

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