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

Beyond the readOnly/idempotent annotations, the description adds useful behavioral context: the output is a binary `.pkpass` file, the operation is scoped to `passes:download`, and the same billing and rate limits apply. It also warns against inventing other paths, which is valuable for an AI agent. It does not describe failure behavior for inactive passes, but annotations already cover the safety profile.

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 mostly tight and front-loaded, with the key action stated immediately. The first sentence 'Download a .pkpass file' is somewhat redundant with the second sentence 'Downloads the `.pkpass` binary...' but the overall length is still appropriate. The endpoint mapping and anti-hallucination note are useful and earn their place.

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 download operation, the description covers the essential context: what is downloaded, for what kind of pass, under what scope, and through which endpoint. The lack of an output schema is mitigated by stating the binary nature of the response. It could be more complete by addressing inactive-pass error behavior, but nothing critical is missing for a safe call.

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 full description coverage for both `id` and `x_app_id`, so the description does not need to repeat parameter details. The description mentions 'active pass' but does not add new semantics to the parameters beyond what the schema documents. This matches the baseline for high schema coverage.

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 clearly states a specific action and resource: downloading the `.pkpass` binary for an active pass. It also maps to a concrete endpoint, which removes ambiguity about the operation. However, it does not explicitly contrast itself with sibling tools like `downloadPassBySerial` or `downloadSharedPass`, so differentiation is only inferred from the path and parameter schema.

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 implies usage for active passes and identifies the exact endpoint, but it does not explicitly state when to prefer this over alternatives. There is no when-not-to-use guidance or mention of sibling tools. The 'active pass' condition and the `{id}` path provide only implied usage context.

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