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

Annotations already declare write, non-destructive, non-idempotent and open-world behavior, so the description only needs to add context. It does contribute the underlying endpoint (POST /api/v3/customers) and reinforces the write nature, but says nothing about duplicate handling when a customer with the same email already exists, which is the key behavioral risk for a non-idempotent create.

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 compact clauses plus an endpoint reference; the write marker and required-field note are front-loaded and every fragment 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 agent does not learn what the call returns (e.g., a new customer ID usable in bookafy_create_appointment), nor how to recover from a duplicate-email failure. For a create tool that is typically chained into a booking flow, that is a meaningful 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%, including the nested custom_fields example with underscore naming, so the schema carries the parameter burden. The description's restatement that name is required and email/phone/custom_fields optional adds no meaning beyond what the schema already documents.

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 ('add a customer record') and immediately delimits scope against the sibling it is most likely confused with: 'It does not book anything.' An agent can distinguish it from bookafy_create_appointment and bookafy_update_customer without opening the 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?

Gives clear selection context by excluding the booking behavior, which is the main ambiguity for a customer tool in an appointments API. It stops short of naming the alternative ('use bookafy_create_appointment to book') or stating prerequisites, so an agent must still infer the ordering relative to appointment creation.

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