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

Goes well beyond the annotations: discloses the $0.40 price, the api_key-vs-x402 payment paths, that unanswerable queries are refused free (coverage_gap, no_charge), a per-IP rate limit of 3 free calls per day shared with the answer tools, and precisely what the optional receipt does and does not represent. This is exactly the payment/limits/error context annotations cannot carry.

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?

Front-loaded with the question it answers, which is good. But the single run-on paragraph packs pricing, coverage lists, rate limits, receipt disclaimers and cross-references into nested parentheticals, making it dense and harder to scan than it needs to be.

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?

With an output schema present, return values need no explanation, and the description more than covers coverage gaps, payment mechanics, rate limits and receipts for a 9-parameter tool. The only missing piece is the boundary against compute_statutory_interest, which an agent could mistake for this 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?

Schema description coverage is 100%, so the baseline is 3, but the description adds a non-obvious constraint the schema never states: due_date is an alternative to invoice_date paired with terms_days. It also clarifies the receipt flag semantics ('on a paid success') that the schema only partially captures.

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?

States a specific computation with concrete outputs: is the invoice overdue, by how many days, and how much statutory late-payment interest (Actual/365 simple, rate and workings cited). The country coverage list and the 'statutory interest only / no late-payment regime' clause narrow the scope. It never distinguishes itself from the sibling compute_statutory_interest, which is the main ambiguity an agent would face.

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 tells the agent how to call it ('Send due_date, or invoice_date with terms_days') and names verify_answer_receipt for receipts, which is useful routing. However, it gives no when-to-use/when-not against the closest sibling (compute_statutory_interest) or the other charge/compute tools, leaving selection to inference.

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