compare_true_costCompare two cars' true monthly cost of ownership: which is cheaper, by how much per month and per year, and which cost line accounts for most of the gap. Differences under $10 a month are reported as a tie.
| Name | Required | Description | Default |
|---|---|---|---|
| a | Yes | First car slug | |
| b | Yes | Second car slug |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover read-only, idempotent and closed-world traits, so the description's main value-add is the tie threshold ('differences under $10 a month are reported as a tie'), a real behavioral rule not present in any structured field. It also discloses the reported outputs, though error behavior for invalid slugs is unstated.
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?
A single sentence with no filler, front-loading the comparison verb and resource before listing the returned facts and the tie rule. Every clause 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?
With no output schema, the description does the work of describing the return contents (cheaper car, monthly/yearly delta, largest contributing cost line), which is a substantial and adequate disclosure. Only the tie-threshold caveat is covered; input failure handling and cost-line enumeration are not, so it falls just short of complete.
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% and both parameters are documented as 'first/second car slug' with a slug pattern, so the schema carries parameter meaning. The description adds only that two cars are compared, which is already implied by the required 'a'/'b' pair.
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 resource ('Compare two cars' true monthly cost of ownership') and enumerates the exact outputs: which is cheaper, gap per month/year, and the dominant cost line. An agent can distinguish this from the single-car sibling get_true_cost purely from the description.
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 two-car comparison context is clearly implied, but the description never says when to prefer this over get_true_cost (single car) or cost_index, and gives no exclusions or prerequisites. Usage is inferable rather than stated.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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