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

Annotations already indicate readOnlyHint=true, and the description adds useful scope information: only paid expenses are counted, and the time window is today and month-to-date. However, it does not describe the return format, whether the result is a single total or separate numbers, or behavior when there are no expenses.

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 a single sentence, front-loaded with the core question 'How much you have spent', and contains no filler or redundant wording. Every word contributes to meaning.

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 zero-parameter read-only summary tool, the description provides sufficient detail to understand the tool's purpose and invoke it correctly. The lack of an output schema means the description could ideally clarify the return shape (e.g., two totals vs. one), but this is a minor gap for such a simple tool.

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 tool has zero parameters and schema description coverage is 100%, so there is no parameter burden for the description to carry. The baseline of 4 applies because the schema fully covers an empty parameter set.

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 tool as a summary of paid expenses, with a specific scope (today and this month so far). It uses a clear 'have spent' action on the 'expenses' resource and is distinguishable from siblings like create_expense_draft or search_expenses, though it does not explicitly name alternatives.

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 for checking how much has been spent today and this month so far, but it does not state when to use this tool versus alternatives, nor does it provide any exclusion criteria. The context is clear enough but not explicit.

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