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

Beyond the annotations, the description adds valuable behavioral detail: the report is computed live, an invoice is overdue only when status is sent and due_date is before today, balances are separated by currency, and no conversion or combined total is produced. This is exactly the kind of edge-case context an agent needs to interpret the output correctly.

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 sentences, no filler, and the core action is stated first. Every sentence earns its place: the summary, the live/overdue logic, and the currency handling.

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 report with no output schema, the description covers the essential semantics: scope, live computation, the precise overdue condition, and how currency balances are presented. Nothing critical is left unexplained.

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 has zero properties, so there are no parameter semantics to document. The schema coverage is effectively 100% because no parameters exist, making the baseline 4 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 opens with a specific verb and resource: it summarizes the caller's unpaid invoices by past-due age. It clearly distinguishes itself from siblings like get_invoice and list_invoices by framing itself as a live, owner-scoped aging report rather than a single-invoice fetch or raw invoice list.

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 gives clear context for when this tool is appropriate: a read-only, owner-scoped report computed live. It does not explicitly name alternatives such as list_invoices or get_invoice, but the scope and purpose are specific enough that an agent can infer when to reach for it versus fetching invoice details.

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