Add a new customer record to your invoicing system. Supply a name (required) plus optional email, phone, and currency so you can start billing them.
Create a new customer.
| Name | Required | Description | Default |
|---|---|---|---|
| name | Yes | ||
| No | |||
| phone | No | ||
| currency_id | No | Defaults to 1 (the company's base currency). |
Changes observed during successful MCP inspections.
v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations are absent, so the description carries the full burden. 'Create a new customer' reveals nothing about whether the operation requires specific permissions, whether it triggers side effects like sending a welcome email, whether duplicate customers are allowed, or what happens on failure. This is critically thin for a mutation tool.
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 single sentence is extremely concise, but it is under-specified rather than efficiently informative. There is no waste, yet the brevity comes at the cost of useful detail.
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 4-parameter creation tool with no annotations, no output schema, and sparse schema documentation, the description is wholly inadequate. An agent has no information about required versus optional fields, side effects, or return values.
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 25%: email, phone, and name have no descriptions, and the only parameter documented is currency_id. The description adds no information about expected formats, defaults, or which fields are required, 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 clear verb (create) and resource (customer), which is specific enough to distinguish it from get_customer, update_customer, and delete_customer. The description is minimal but unambiguous about what the tool does.
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?
No guidance on when to use this tool versus alternatives such as update_customer or when a customer already exists. It does not mention prerequisites, required fields beyond the schema, or any conditions under which creation should occur.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.