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

readOnlyHint=true already tells the agent this is a safe read, so the description's remaining burden is light. It adds that related resources can be embedded via zoom and cites the underlying endpoint, but says nothing about not-found behavior or the cost of zooming multiple 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 tight sentences: the core operation first, then the optional zoom behavior and endpoint. Every clause carries information and nothing is repeated from the title or schema.

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 read-only single-record fetch with fully documented parameters and a readOnlyHint annotation, the description gives an agent enough to invoke it correctly. It does not cover return shape or error cases, but that gap is small for a getter of this simplicity.

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, but the description earns credit by giving concrete zoom values (default_billing_address, subscriptions) that the schema's generic 'Comma-separated related resources to embed' does not enumerate. The id parameter gains nothing 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?

States a specific verb and resource ('Get a single customer by id') and scopes it to a single record, which implicitly separates it from the foxy_list_customers sibling. It does not explicitly name any sibling, so differentiation is inferred rather than stated.

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 (fetch one customer when you have an id) and mentions optional zooming, but never states when to prefer this over foxy_list_customers or when zoom is warranted versus a follow-up call. Usage is implied, not spelled out.

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