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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive). The description adds useful context: the required OAuth scope (`passes:read`), the exact GET mapping, and the operational caveat about shared PassFast API billing and rate limits. No contradiction with annotations.

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 short, purpose-driven paragraphs with the headline action first and supporting detail in order of importance. No filler or repetition of obvious schema facts; each line adds behavioral or routing context.

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?

For a three-parameter read-only lookup, the description gives the endpoint, scope, wallet selection logic, and API constraints; the input schema already documents all parameters. It slightly undersells the return shape ('full details' without a schema/field list), but that is not necessary for correct invocation.

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 100%, so baseline is 3, but the description adds value by indicating that serial_number is a path parameter (via GET /manage-passes/serial/{serial_number}) and that wallet_type is a query parameter with a default behavior. The wallet_type disambiguation sentence reinforces the enum's purpose beyond the schema text.

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 clear verb and resource: 'Get a pass by serial number' and 'Returns the full details of a single pass'. The OpenAPI operation and GET path make the lookup-by-serial scope explicit, separating it from siblings like listPasses or downloadPassBySerial. Could have named an alternative, but the resource and path are unambiguous.

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?

Provides clear context for the wallet_type parameter ('when a serial has both Apple and Google passes') and states scope, billing/rate limits, and the exact endpoint. It does not explicitly compare this tool with alternatives such as getPass or downloadPassBySerial, so when-to-use-this-vs-that is implied rather than stated.

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