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

The annotations already establish that the tool is read-only, idempotent, and non-destructive. The description adds useful behavioral context: the default wallet_type is `apple`, the scope is `passes:read`, and it maps to a specific GET endpoint with normal PassFast API billing and rate limits.

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?

The description is front-loaded with the core purpose and then adds relevant usage details about wallet_type, scope, and endpoint mapping. The operational caveats about billing and not inventing paths are somewhat boilerplate, preventing a perfect conciseness score, but the overall length is reasonable and well-organized.

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 simple read-only GET lookup, the definition is largely complete: all parameters are well documented in the schema, annotations cover safety, and the description explains the key wallet_type behavior. It could be slightly more complete by describing the response shape or explicitly routing agents to getPass when they have a pass ID, but those are 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 input schema already provides 100% description coverage, including serial_number uniqueness, wallet_type enum/default, and x_app_id override semantics. The description mostly restates the wallet_type default rather than adding new parameter meaning beyond the schema, so the baseline score of 3 is appropriate.

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 opens with a specific verb and resource: 'Get a pass by serial number', then elaborates with 'Returns the full details of a single pass looked up by serial number.' This clearly differentiates the tool from sibling pass-lookup tools by identifying the exact lookup mechanism, and the OpenAPI mapping reinforces the unique endpoint.

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 gives clear context: this tool is for retrieving a pass when a serial number is known, and it explains how to handle the Apple/Google wallet ambiguity via `?wallet_type=`. It does not explicitly name sibling alternatives like getPass or state when not to use this tool, so it misses the highest bar for alternatives guidance.

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