Add a customer. Money is integer minor units (cents). Calling this changes nothing: it returns a preview of what would change and a confirmation link. Only the merchant, on that page, can make it happen.
| Name | Required | Description | Default |
|---|---|---|---|
| Yes | |||
| notes | No | ||
| phone | No | ||
| address | No | ||
| lastName | No | ||
| firstName | No | ||
| acceptsMarketing | No | Only when the person agreed to it. |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Goes well beyond the annotations by disclosing that the call is a non-mutating preview requiring merchant confirmation on a separate page, which explains why readOnlyHint=false despite the name. The 'Money is integer minor units (cents)' sentence is irrelevant here since this schema has no monetary parameters, and no auth or rate-limit behavior is mentioned.
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?
Purpose and the preview semantics are front-loaded, and the prose is tight overall. But the money-units sentence earns nothing for this tool and dilutes an otherwise well-structured three-sentence definition.
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 useful work by describing what the call returns (a preview of changes and a confirmation link). Yet for a seven-parameter create tool with a nested address object and near-zero schema documentation, the field-level semantics are left entirely unexplained.
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 only 14% (just acceptsMarketing), so the description carries the burden for seven parameters, including a nested address object, and it provides none of that. Its one parameter-adjacent sentence concerns money units, which no parameter in this schema uses, so it fails to compensate for the coverage gap.
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') and immediately corrects the expectation by explaining it only produces a preview plus a confirmation link. That makes the tool distinguishable from customers_lookup, customers_delete, and other customer siblings, though it never names a sibling 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?
The sentence 'Only the merchant, on that page, can make it happen' implies the agent should call this to propose a change rather than to complete one, which is useful context. However there is no explicit when-to-use/when-not guidance and no routing to alternatives such as customers_lookup for duplicate checking.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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