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

readOnlyHint=true already tells the agent this is a safe, non-mutating read, so the bar is lower. The description adds the returned field groups, but says nothing about 404/not-found behavior, id formats, or auth requirements beyond the endpoint path.

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 short clauses: the capability plus its return payload, then the underlying endpoint. Front-loaded, zero filler, and the trailing 'GET /v3/customer/:id' aids mapping without bloating the text.

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?

With no output schema, the description usefully compensates by naming the field groups returned. For a one-parameter read-only tool this is nearly sufficient; only error/not-found semantics are omitted, a minor gap.

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% for the single customerId parameter, so the baseline is 3. The description confirms the id is what identifies the record but adds no format, prefix, or sourcing detail (e.g., where an agent obtains a valid id) 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 ('Fetch a single customer by id') and enumerates the payload it returns (contact details, emails, phones, vehicle/order/appointment counts). The 'single ... by id' framing cleanly separates it from shopmonkey_search_customers, find_customers_by_email, and find_customers_by_phone without opening any 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?

'By id' implies the caller must already hold a customer id, which faintly contrasts with the lookup-style siblings, but the description never names those alternatives or states when to prefer this over search_customers/find_customers_by_*. Usage is inferable rather than stated.

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