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

While annotations cover readOnlyHint, the description adds crucial behavioral context not present in the structured data: it discloses that the data 'contains personal data' (a sensitivity requirement) and specifies the exact API endpoint format ('GET /customers/{customer_id}').

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 definition is extremely concise, using two short, highly efficient sentences to cover the core function, the optional data behavior, and the technical method/resource path without any 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?

Given that this is a simple GET operation, the description provides all necessary context: it retrieves a single entity, uses a customer ID, handles optional custom field expansion, and flags the nature of the data. No critical information is missing.

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?

Since the input schema coverage is 100%, the structured schema provides comprehensive semantic definitions for all parameters. The description does not add any clarifying meaning or constraints to the specific parameters.

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 clearly identifies the action ('Get'), the resource ('customer'), and the primary retrieval method ('by id'). It effectively distinguishes this single-fetch operation from list operations present in the sibling tools.

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 usage: use this when a specific customer ID is known. However, it does not explicitly state 'use this instead of list_customers' or provide clear exclusionary criteria for other retrieval methods.

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