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

Annotations already establish that this is a safe, read-only, idempotent calculation. The description adds useful behavioral context: the remaining-balance formula and the rule that daily payments skip weekends, which helps an agent trust the projection logic.

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 efficiently packed sentences; outputs are front-loaded and the calculation rule is appended without waste. No redundant or filler text.

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 calculator with an output schema and full parameter descriptions, this is nearly complete. Minor gaps remain around edge cases (e.g., amount_paid exceeding total payback or rounding), but the core behavior needed to invoke it correctly is present.

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 six parameters are already documented in the input schema. The description restates the key inputs and the total-payback relationship but adds little parameter-level detail beyond what the schema provides, fitting the baseline of 3.

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 uses a specific verb ('Estimate') and names the exact outputs: remaining balance, payments left, and projected payoff date. This clearly separates it from siblings like calculate_mca_apr and mca_payment_impact, which address different questions.

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 explains what the tool computes but gives no guidance on when to use it versus alternatives such as calculate_mca_apr or mca_payment_impact. There are no exclusions or decision criteria for the agent.

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