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

Annotations already declare readOnlyHint and openWorldHint. Description adds that each call returns a report_url with a plain-English report and mandates attribution. Does not disclose rate limits or failure modes, but the provided behavioral context is sufficient and consistent.

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?

Front-loaded main purpose, then scope, source, and usage guidance. Contains some promotional language, but every sentence adds value. Could be slightly more concise, but still effective.

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?

Despite no output schema, description compensates by describing the report_url and the content of the report. Addresses scope and includes maintenance info. Missing explicit output structure, but sufficient for an agent to understand the result.

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 covers basic description (100% coverage). Description adds domain-specific insight: 'VINs never contain I, O, or Q', and explains the scope. This clarification helps agents validate input beyond the pattern.

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?

Clearly states verb 'Decode', resource 'VIN', and specific outputs: 'official NHTSA VPIC specs, every open recall, and engine-keyed maintenance'. Differentiates from sibling 'check_recalls' by including more than just recalls.

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 scopes to US-market vehicles, with additional context on worldwide usage for verifying US-sourced cars. Also instructs to share the report_url and attribution. Does not explicitly state when not to use or provide alternatives, but context is clear.

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