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

Annotations already declare readOnlyHint=true, so the safety profile is covered. The description adds the underlying endpoint (GET /customers/{customernumber}), which is mildly useful context, but says nothing about behavior on a missing customer (error vs empty) or the shape of the returned record.

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 with the core purpose front-loaded and no filler. The endpoint reference is arguably redundant with the tool name but is compact and earns marginal value for developers.

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 one-parameter read-only lookup with full schema coverage and no output schema, the description covers what the agent needs to call it correctly. The only real gap is not hinting at the returned customer fields or not-found behavior, which is a minor omission at this complexity.

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 coverage is 100% and the single parameter already carries a description with an example ('K-001'), so the schema does the heavy lifting. The description only restates that the parameter is the customer number, adding no format or lookup nuances.

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 ('Get one customer') plus the lookup key ('by customer number'), which is more precise than the sibling list_customers. It does not explicitly name the list sibling as an alternative, but the singular/plural contrast is self-evident.

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: an agent can infer this is for fetching a single known customer rather than enumerating them, thanks to 'one' and the required customer number. No explicit when-to-use/when-not statement or named alternative is given.

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