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

readOnlyHint=true already declares this as a safe read. The description goes further by disclosing the underlying endpoint (GET /customers/{id}) and, importantly, the exact fields returned — significant since no output schema exists. It stops short of describing error behavior for an invalid ID or any response envelope details.

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, no filler: the identity/scope and field list lead, the optional include behavior follows, and the endpoint reference is appended. Every clause earns its 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?

With no output schema, the description compensates well by listing the returned fields and the optional VIP expansion. Minor gaps remain around failure modes and whether the include parameter is required for VIP data, but nothing essential for a correct invocation is missing.

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 coverage is 100%, so the baseline would be 3. The description adds real meaning by explaining that the optional payload is VIP status with current and next tier, which maps the include enum values to a concrete outcome for the caller.

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 (fetch), a single-resource scope (one customer) and the key identity key (Smile customer ID), which cleanly separates it from the sibling smile_list_customers. It also enumerates the returned fields, so an agent knows what it gets without opening anything else.

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?

Implicit usage is discernible: 'one customer by ... ID' versus the list siblings, and the optional include parameter is hinted at. However, no explicit when-to-use/when-not or named alternative is given, so the routing to smile_list_customers or smile_get_customer-adjacent tools is left to inference.

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