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

Annotations already mark this as readOnly=true, and the description adds behavioral detail beyond that: it specifies the sort order ('newest first'), the exact HTTP endpoint, and the response wrapper ('{ data,pagination } when more pages exist'). This is useful context for understanding how the tool behaves at runtime without contradicting the read-only hint.

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 description is extremely concise, with three short sentences that front-load the core purpose and then add the API endpoint and response wrapper. Every clause adds information and no filler is present. The structure makes it easy to scan quickly.

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 read-only list tool with no output schema and six parameters, the description covers the key behavior: entity, ordering, endpoint, and response shape. It does not describe the individual fields of an expense or go into pagination mechanics, but those are largely covered by the schema's parameter descriptions. The response wrapper is a helpful addition that compensates for the absent 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?

The input schema covers 100% of the parameters with descriptions, so the description does not need to explain them. The description does not add any parameter-specific meaning beyond the schema, which is acceptable given the high schema coverage. Baseline of 3 is appropriate.

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 states a specific action and resource: 'List expenses (bills you received), newest first.' It also provides the API endpoint (GET /expenses), eliminating ambiguity about what the tool operates on. The parenthetical distinguishes expenses from related siblings like list_invoices or list_receipts.

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 phrase '(bills you received)' gives clear context that this tool is for incoming bills, implying a distinction from invoice or receipt listing tools. It also communicates ordering behavior ('newest first') and the pagination wrapper, which helps an agent know when to use pagination parameters. However, it does not explicitly name alternative tools or state when not to use this one, so it stops short of a 5.

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