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

Annotations already declare that this is a non-readonly, non-idempotent, non-destructive operation. The description adds valuable behavioral context not in the annotations: it requires a claimed Last Price credential and a claimed workspace, and specifically warns that a sandbox self-registration key is refused with 403 until a person claims the workspace.

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?

The description is two tight sentences, front-loads the action and parameters, then gives the prerequisite caveat. Every sentence carries useful information with no redundant filler.

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 description covers the basic call shape and important auth/workspace prerequisites, but with no output schema it does not explain what is returned after creation. It also omits duplicate/uniqueness behavior for email or external_id, which matters for a create operation with external identifiers.

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 four parameters are already documented in the schema and the baseline is 3. The description restates that name is required and email, external_id, and metadata are optional, but adds little semantic detail beyond what the schema already provides.

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?

The description states a specific verb and resource ('Add a customer') and lists the created fields, making the core operation clear. It does not explicitly distinguish itself from nearby siblings such as create_contact, update_customer, or get_customer_by_external_id, so it falls short of full sibling differentiation.

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 description implies the tool is for creating a new customer and states prerequisites about a claimed credential and workspace. It does not say when to use this versus update_customer, get_customer_by_external_id, or create_contact, and it gives no explicit exclusions.

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