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

The annotations already declare readOnlyHint=true, and the description aligns with that by saying 'Fetch' and specifying GET /expenses/{id}. The endpoint adds mild operational context, but no extra behavior such as error handling or response shape is disclosed.

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 crisp sentences with no fluff. The core action is front-loaded, and the API endpoint is a helpful, non-redundant addition.

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 single-parameter read-only getter, the description covers the essential selection and invocation details. However, there is no mention of potential error responses or what the returned expense object contains, which would be more important given there is no output schema.

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 id parameter is described, but the description adds the useful fact that the id is used as a path parameter in GET /expenses/{id}. This goes slightly beyond the schema's generic 'resource id' wording.

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 uses a specific verb and resource ('Fetch a single expense by id') and clearly distinguishes this from list-oriented siblings like list_expenses. The API endpoint reinforces the exact operation.

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 when a single expense ID is known, but it does not explicitly contrast with list_expenses or other alternatives. There is no 'use this instead of X when...' guidance, leaving sibling differentiation to inference.

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