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

Beyond the readOnly/idempotent annotations, the description explicitly states it does not make payments, change accounts, fetch external data, or retain tool inputs. This gives agents a clear, non-destructive mental model and matches the annotations exactly.

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 front-loaded with the primary use case and return value, followed by differentiation and behavioral caveats. Every sentence contributes distinct information without redundancy or filler.

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 calculation tool, the description covers purpose, output, prerequisites, sibling distinctions, and side-effect guarantees. It is fully sufficient for an agent to decide when and how to invoke it correctly.

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 rich parameter descriptions already present, so the baseline applies. The outer description only restates APR requirements and minimum-payment fallback, adding little semantic value beyond the schema.

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 opens with concrete use-case examples ('if I pay $200 a month...') and clearly states the output: payoff duration and interest paid. It also distinguishes this cost-question tool from reporting-oriented siblings like get_reported_snapshot and simulate_paydown.

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?

It explicitly says when to use the tool ('Use this for...') and when not to, pointing to get_reported_snapshot or simulate_paydown for reporting questions. It also provides a prerequisite (purchase APR) and the consequence of omitting it, leaving little room for misuse.

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