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

The readOnlyHint annotation already establishes this as a safe read operation. The description adds useful behavior beyond that: it names the HTTP endpoint (GET /customers/{id}) and documents the optional 'zoom' behavior that embeds related resources.

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?

Two sentences with no filler. The core action is front-loaded, and the endpoint reference is brief and informative.

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 single-resource read tool, the description plus annotations and complete schema coverage are nearly sufficient. It does not explicitly describe the return payload, but no output schema exists and the GET endpoint strongly implies the customer object is returned.

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 description coverage is 100%, so the baseline is 3. The description adds value by giving concrete zoom examples (default_billing_address, subscriptions…) and clarifying the request format via the endpoint, going slightly beyond the schema.

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?

Description states a specific verb and resource: 'Get a single customer by id'. The qualifier 'single' and reliance on an id clearly distinguish it from sibling list tools, and the optional zoom behavior adds further precision.

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?

Clear usage context is provided: use this to fetch exactly one customer by id. It does not explicitly name alternatives like foxy_list_customers for bulk retrieval or foxy_update_customer for mutations, but the contrast is strongly implied by 'single... by id'.

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