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

With readOnlyHint=true already declared, the description adds useful behavioral context by listing the exact fields returned, including the receipt-attached flag and the meaning of 'SIN JUSTIFICANTE = no file'. It does not describe pagination or ordering, but the schema's limit bounds partially cover that and the tool has no output schema, making the field disclosure especially valuable.

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?

Three dense but well-structured sentences: first the resource and returned fields, then query semantics with an example use case, then the alternative tool for attachment. Every sentence adds information without repetition, and the key scope is front-loaded.

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?

The description covers what the tool returns, which is critical because there is no output schema, and it fully explains the only under-documented parameter (query). It also names the relevant sibling for the adjacent attach action, leaving no major gaps for an agent to call it correctly.

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 query parameter's schema description is minimal ('free text, e.g. supplier invoice number or supplier name'), while the tool description significantly expands its meaning to search across description, invoice number, notes, supplier name/NIF, and amount. The limit parameter is fully specified in the schema with default and min/max, so no additional description is needed.

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 states a specific verb and resource (list expenses/gastos) and immediately enumerates the returned fields (date, description, supplier, total, category, receipt attached), which clearly distinguishes it from mutation siblings such as create_expense or update_expense. It also explicitly routes receipt attachment to attach_expense_receipt, making the scope unambiguous.

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?

It gives a concrete use case ('e.g. to check whether a supplier invoice is already booked') and names the alternative tool for a related but different action ('To attach the receipt file to an expense use attach_expense_receipt'). It does not explicitly say when not to use it (e.g., for invoices use list_invoices), but the main boundary is clear.

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