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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds real behavioral value beyond that: it discloses that a trade-in's tax saving applies only 'where the state credits it', and that the result includes a doc-fee-vs-cap comparison and a total-vs-walk-line comparison — output behavior not visible in the schema.

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 dense sentences that front-load the core computation and then layer optional branches in the order an agent would consider them. No filler, and the size is proportionate to a 22-parameter tool.

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 22 parameters, no output schema, and rich schema descriptions, the description covers the main computation and even the comparative outputs. Gaps are minor: it never mentions the city/county rate-table dependency or that DC and Illinois require extra inputs, which an agent would only discover by reading the 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 coverage is 95%, so the baseline is 3, but the description earns more by tying parameters to outcomes: the trade-in parameter pair is explained via the tax it saves, down payment and loan are framed as producing 'the payment', and the doc fee is framed as being checked against the state cap. It still doesn't touch the DC-only weight/MPG or Illinois buyer-residence switches, leaving those entirely to 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?

States a specific verb and artifact — 'Itemizes an out-the-door estimate for a vehicle price' — then enumerates exactly what goes into it (rebates, doc fee, add-ons, sales tax with rebate/cap rules, title and registration). This is clearly distinguishable from narrow siblings like loan_payment or state_rules because it composes the full OTD figure.

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?

Usage is implied rather than stated: an agent can infer this is the tool for a full out-the-door total when it has a selling price and a state. There is no explicit when-not or routing to siblings (e.g., 'use state_rules first to check which states have city rate tables', or 'use loan_payment for payment-only math'), so the agent must infer boundaries.

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