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

Annotations already establish readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds genuinely useful behavior: batch ordering guarantees, the 50-VIN ceiling, and the non-obvious fact that a bad check digit yields valid=false plus a warning rather than an error.

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?

Four sentences, all front-loaded: purpose first, then per-action parameter rules, then the error-semantics edge case. No sentence is redundant with another and none pads.

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 carries the return-shape burden and does so by listing decoded attributes and the valid=false warning contract. The only gap is the absence of any statement about how this relates to the sibling wenmar_vehicles tool.

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 only 50% (vins and action are undescribed in the schema), yet the description compensates by explaining what vins holds, the 50-item cap, and the decode/batch split. The year override is also clarified as a model-year substitute, adding meaning beyond the schema's phrasing.

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?

Names a specific verb (Decode) and resource (vehicle identification numbers) and enumerates the decoded fields, so the agent knows exactly what comes back. It does not, however, distinguish itself from the sibling wenmar_vehicles tool, leaving that comparison to inference.

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?

Explicitly separates action=decode (single VIN, optional year override) from action=batch (up to 50 VINs, ordered results), which tells the agent which mode to pick for a given input. There is no guidance on when to reach for this tool instead of wenmar_vehicles.

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