count_invoices

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

With no annotations provided, the description must carry the burden of transparency. It implies a read-only operation (counting) but does not explicitly mention side effects, permissions, or edge cases. For a simple count, this is acceptable, but it could be more explicit about returning a numeric result.

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 concise and well-structured, consisting of two clear sentences with no unnecessary details or fluff. It efficiently conveys the purpose and usage.

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?

Given there is no output schema, the description could benefit from stating the return type (e.g., an integer count). However, the phrase 'Count invoices' strongly implies a numeric result, making the tool's behavior sufficiently clear for typical use cases.

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 description adds minimal value beyond the input schema. It merely restates that client and status are optional filters, without explaining their exact semantics (e.g., how client is matched, whether status accepts multiple values). The schema already provides types and enums, so the description contributes little to parameter understanding.

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 that the tool counts invoices, and it explicitly says to use it when the user asks how many invoices exist. This effectively distinguishes it from sibling tools like search_invoices or get_invoice, which return detailed data rather than a count.

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 provides explicit guidance on when to use this tool: 'Use when the user asks how many invoices there are.' It also mentions optional filters, implying it can be used with or without them, which clarifies its flexibility.

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