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

Annotations already declare readOnlyHint=true and destructiveHint=false, covering the safety profile. The description adds value by specifying the scope ('returns no valuation, no comparable listings and no market data') and the additional fields for hybrid/EV vehicles (electrification level, battery/charging facts), which are not in the annotations. No contradiction with read-only semantics.

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 sentences, each earning its place: the first states the primary purpose and outputs, the second adds EV-specific behavior, the third clarifies non-goals. It is front-loaded with the core action and lists attributes efficiently without redundancy or fluff.

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 single-parameter tool with no output schema, so the description must convey what the agent will get. It lists the identity fields, EV specifics, and explicitly states what is excluded. Missing, though not critical, are error handling for invalid VINs and the exact return structure; however, for a decode tool the field enumeration is sufficient. A 4 reflects strong coverage with minor gaps.

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 already provides a description for the 'vin' parameter ('The 17-character Vehicle Identification Number to decode.'), achieving 100% coverage. The tool description repeats the 17-character length and requirement but adds no new semantic meaning beyond the schema. Per the rubric, high schema coverage yields a baseline of 3, and the description does not exceed that.

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 uses the specific verb 'Decode' paired with the resource 'VIN' and enumerates the exact output fields (year, make, model, trim, body style, drivetrain, engine, transmission, fuel type). It also adds electrification details for hybrid/EV, making it unambiguous. The sibling tools (about, pricing, research library) cover entirely different domains, so the tool's distinct purpose is clear without opening schemas.

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 clearly states this is 'Identification only' and explicitly excludes valuation, comparables, and market data, which tells the agent when NOT to use it. However, it does not name an alternative tool (e.g., pricing tool) for those needs, leaving routing to inference. This is clear context without explicit exclusions, so a 4 is appropriate rather than a 5.

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