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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds genuinely non-obvious behavior: several fields are deferred and only materialize via expand (field_values, credit_balance, staff_assignments). It omits error/not-found behavior, but the key competence needed to call this correctly is disclosed.

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?

Three compact clauses with the core action front-loaded and no filler; the expand guidance and endpoint reference follow in dependency order. It is dense but every clause carries information.

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 does the work of listing the return fields and explaining how to obtain deferred ones, which is sufficient for a single-resource read. It lacks any note on failure modes for a bad customer_id, the only clear remaining 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 the baseline is 3. The description earns above baseline by naming endpoint-specific expand targets that the schema's generic example (customer,event.instructors) does not convey, telling the agent which deferred customer fields are actually available here.

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 one customer by id') and enumerates the returned fields, which immediately separates it from goteamup_list_customers and goteamup_get_customer_membership. The endpoint mapping ('GET /customers/{id}') confirms scope for an agent that knows the API.

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 only explicit routing guidance is conditional field expansion ('Use expand for deferred fields'). Nothing states when to prefer this over goteamup_list_customers or goteamup_get_customer_membership, so tool selection is left to inference from the name.

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