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

The readOnlyHint and destructiveHint annotations already signal a safe, non-destructive operation, so the description's job is lighter. It adds meaningful context by clarifying that the tool does not affect what bureaus see and that APR is a hard prerequisite for returning output, which goes beyond the annotations.

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 sentences with no filler: the core computation is front-loaded, followed by user-facing example questions, sibling differentiation, and the critical prerequisite. Every sentence earns its place.

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 estimation tool with a rich input schema and an output schema, the description covers purpose, typical user intent, exclusions, and the one prerequisite that could cause a failed call. Nothing needed to select or invoke the tool correctly is missing.

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%, so the description doesn't need to restate every field. It adds value by surfacing the relationship between APR and the answer, warning that missing APR yields no timeline, and mapping user phrasing like 'pay $200 a month' and 'pay the minimum' to the monthlyPayment parameter.

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 precise calculation — how long a card takes to clear at a fixed monthly payment plus interest cost — and explicitly labels it a cost question, not a reporting one. This distinguishes it clearly from reporting-focused siblings and leaves no ambiguity about the resource or behavior.

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?

Names the alternatives reported_snapshot and simulate_paydown for reporting-focused scenarios, and states a hard prerequisite: purchase APR must be present or no timeline is returned. An agent gets both when-to-use and when-not-to-use guidance explicitly.

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