get_invoice_pay_preview

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

Without annotations, the description bears full responsibility. It declares 'Read-only; consumes nothing' and explains the consumption priority. This covers the key behavioral trait, though it could mention edge cases like insufficient balance or already-paid invoices.

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 concise sentences: action description, read-only note, and usage instructions. Every sentence adds value without redundancy or fluff.

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 lacks details on the return value structure (e.g., breakdown fields). Given no output schema, the agent might need more context on what the preview outputs. However, for a simple preview tool, the current info is sufficient but not complete.

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?

Schema coverage is 100% for the single 'id' parameter, which has a clear description. The description repeats this guidance but does not add extra semantic meaning beyond what the schema provides, meeting the baseline.

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 the tool previews paying an invoice from account balance, detailing consumption order (promo bonus, real credit, shortfall). It distinguishes itself from sibling tools like get_invoice or get_credit_balance by focusing on a specific payment preview scenario.

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?

Explicit instructions: 'Pass an invoice id from list_invoices. Use before discussing a "pay from balance" action.' This provides clear context for when to use the tool and implies not to use it for actual payment, as it is read-only.

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