What a diagnostic trouble code (P0420, U0100, …) means where the OBD-II standard defines it, and — the part no other source publishes — which vehicles' federal record actually names it: how many manufacturer service bulletins and owner complaints mention it, and on which model years.
| Name | Required | Description | Default |
|---|---|---|---|
| code | Yes | A trouble code, e.g. P0420. |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description must carry the behavioral transparency burden. It discloses that the tool provides both standard OBD-II meanings and federal record counts (how many bulletins/complaints). It does not mention any limitations or behavior on invalid codes, but for a lookup tool with a single string input, this is acceptable. The description provides some behavioral context beyond 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?
The description is concise, with a single sentence that packs key information. It front-loads the core definition and then adds the unique value proposition. It avoids redundancy and is easy to scan, though the sentence is a bit long with a parenthetical and em-dash, which slightly reduces readability.
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?
Given the simplicity (1 parameter, no output schema), the description is quite complete. It tells the agent what the tool returns (meaning and federal record counts) and provides example codes. It does not describe the output format, but the absence of an output schema and the simplicity of a lookup tool make this acceptable. The description covers the essential context an agent needs to decide if this tool fits the user's query.
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?
The schema coverage is 100% for the sole parameter 'code', and the description provides an example format ('P0420') and clarifies it expects a trouble code. The description adds marginal value by naming specific examples and implying the format, but the schema already describes it as a trouble code. Baseline of 3 is appropriate.
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 clearly states the tool's function: it defines OBD-II trouble codes and provides unique federal record data (service bulletins and complaints) with specific examples (P0420, U0100). It distinguishes itself from sibling tools by emphasizing the unique data source, making it clear this is not a generic code decoder.
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 description implies the tool is for looking up trouble codes, but it does not explicitly state when to use it versus siblings. However, the unique offering (federal record data) implies a specific use case, and a clear contrast with siblings is not needed since the siblings are unrelated (e.g., VIN decoding, recalls). Still, no explicit guidance on when not to use it is given.
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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