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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds useful behavioral context that the expansion of contacts/phones/emails/locations/custom_fields is optional and multiplicative on payload size, plus the underlying endpoint. It says nothing about error behavior for a missing id or permissions.

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 sentences, both front-loaded: the scope of the read comes first, the optional expansions second, and the endpoint last. The trailing 'GET /customers/{id}' is near-redundant but costs almost nothing and clarifies the REST mapping.

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?

The tool is a simple single-resource read with a fully described schema and read-only annotations, so the essentials are covered. However, there is no output schema and the description does not indicate the shape of the returned customer object or how sparse fieldsets via 'fields' affect it, leaving a small but real 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%, so all three parameters are already documented in the schema with an enum list for expand and a pattern example for fields. The description only restates the expandable resources, adding no syntax or constraint meaning beyond the schema; baseline 3 is appropriate.

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 ('get') and singular resource ('one customer by id'), which clearly separates it from the sibling servicefusion_list_customers. It does not explicitly name any sibling, but the singular-vs-list distinction is legible from 'one customer by id'.

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?

There is no when-to-use guidance and no named alternative; the agent must infer on its own that list_customers is the choice when the id is unknown. The only implicit signal is 'by id', which leaves prerequisite discovery to inference.

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