Validate VIN check digit (offline)

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

With no annotations, the description carries the full burden and does well: it discloses that the operation is pure local math with no network call, and sets an important expectation boundary — a valid checksum proves well-formedness but not manufacturer issuance. It stops short of stating the return shape or failure behavior, which matters given there is no output 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 short sentences, each earning its place: the mechanism, the practical benefit, and the critical caveat. The mechanism is front-loaded and nothing is redundant.

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?

The validity caveat is exactly the kind of context an agent needs before acting on the result, and the offline/no-network behavior is fully covered. The one gap is the return value (boolean pass/fail vs. an error), which is not described and cannot be inferred since no output schema exists.

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% for the single 'vin' parameter, so the schema already documents the input. The description adds no syntax, format, or length constraints beyond what the schema states (uppercasing, whitespace stripping), so the baseline of 3 applies.

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 — verify a VIN against the ISO 3779 / 49 CFR §565.15 check-digit checksum — and names the exact standard applied. It is clearly distinguishable from decode_vin and buy_vin_report by being an offline validity check rather than a data lookup.

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 positions the tool as a pre-flight typo check 'before consuming a paid API call,' which effectively routes the agent away from the costlier buy_vin_report sibling. It does not name the sibling tools directly or state exclusions (e.g. when decoding is still required afterward), so it falls short of full when/when-not guidance.

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