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

With no annotations, the description carries the full behavioral burden. It does disclose that sales tax, trade-in, and down payment are included, but it introduces a major ambiguity: it says 'latest CDN sales tax rates' while the schema says 'US state for sales tax lookup.' It also does not explain edge cases like missing state/province, defaulted rates, or output structure.

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 appropriately short and front-loaded with the main outputs first. Every clause adds relevant information, though the ambiguous 'CDN' abbreviation and the tax-rate claim could confuse more than they help.

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?

This is a 7-parameter tool with no output schema and no annotations, so the description needs to do substantial work. It summarizes outputs and inputs at a high level but fails to reconcile 'CDN sales tax rates' versus 'US state', omits default behaviors (loanTermMonths, salesTaxRate), and lacks enough detail for an agent to correctly choose and invoke it with confidence.

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 the schema already documents every parameter. The description adds some value by naming the included factors (sales tax, trade-in, down payment, amortization), but it does not clarify parameter-specific semantics beyond what the schema provides, and its tax-rate source claim conflicts with the schema's US-state wording.

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 names a specific verb and resource ('calculate' a car loan) and states the core outputs: monthly payment, total interest, and amortization. It is clear enough to distinguish from most siblings, though it does not explicitly contrast with similar tools like calculate_mortgage or calculate_student_loan.

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?

There is no guidance about when to use this tool versus alternatives. The name and phrase 'car' imply use for auto loans, but the description never states exclusions or names alternative siblings for different loan types, leaving the decision to inference.

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