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

Annotation coverage is thin — only destructiveHint=true — so the description must add value, and it does state this is an additive write ('This ADDS data to your account'). It does not mention authentication, rate limits, whether a duplicate email fails, or idempotent retry behaviour, so it only partially fills the gap.

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 plus an endpoint reference; the mutation nature is front-loaded with no filler. The all-caps emphasis and the raw endpoint string are slightly noisy but do not waste much space.

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?

For a 6-parameter creation tool with full schema coverage and no output schema, the essentials are present: what is created, that it is a write, and what the record is used for. Missing pieces are the response shape (e.g. returned customer id) and the duplicate-email/idempotency consequences, which an agent would want before retrying.

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% and each field (name, email uniqueness, phone shape, default instrument id, metadata, idempotency key) is documented in the schema itself. The description adds no parameter-level detail beyond the schema, so the baseline of 3 applies.

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 ('CREATES a customer record') and clarifies the business role of the record — a container for saved instruments and future payments. That is enough to distinguish it from the payment/refund/list siblings, though no sibling is named explicitly.

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?

Usage is only implied via the parenthetical about attaching saved instruments and future payments, which hints at when a customer must exist first. There is no explicit when-to-use vs when-not, and no mention of prerequisites such as calling get_customer first to avoid duplicates (despite email needing to be unique).

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