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

Annotations only cover safety and idempotency, so the description carries substantial weight. It discloses key behavioral nuances: transactions are not in the bill payload, opt-in cost, transactions_basis semantics, the authoritative nature of totalAmount, and the non-obvious meaning of payments[] in Brazilian Open Finance. No annotation contradiction exists; the description adds rich context.

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 long but every sentence earns its place, given the nuance of the endpoint. It is structured logically: base fields, optional transaction enrichment, transaction basis explanation, important payment caveat, and pointers to sibling tools. The density is justified and well 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?

With no output schema and zero schema description coverage, this description carries the full explanatory burden. It covers return fields, batch shape, transaction linking logic, authoritative amount handling, an extra scan cost, and how to derive payment status. This is exhaustive enough for an agent to invoke the tool correctly without external documentation.

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 0%, so the description must compensate. It clearly explains bill_ids as an array requiring prior list discovery, account_id as the credit card account needed for transaction inclusion, and include_transactions including its cost and effects. However, the transactions_detail enum parameter is not explained in the description, leaving one of four parameters underspecified.

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 immediately states the action and resource: returns bill-level detail for one or more credit card bills by id. It names the specific fields returned and explicitly differentiates from sibling tools by noting that list tool should be used for discovery and list transactions for fetching transactions separately. This is clear and high-signal.

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 explicit usage direction: call openfinance_list_credit_card_bills first to discover ids, optionally pass include_transactions to enrich responses, or use openfinance_list_transactions for manual transaction fetching. It also warns when not to assume paid status and points to the sibling tool that derives payment_status. This is excellent routing guidance.

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