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

Annotations already declare readOnlyHint=true and destructiveHint=false, but the description goes far beyond that. It discloses the transactions_basis estimation logic (bill_id vs date_window vs unavailable), the cost of the opt-in ('extra full transaction scan'), the authority of totalAmount (do NOT rebuild by summing), the semantics of payments[] (which may refer to the previous bill), and the lack of a paid field in Pluggy. This is rich behavioral context that prevents misinterpretation.

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 densely packed with essential details. Critical info is front-loaded (what it returns and the main parameters), followed by opt-in behavior, estimation logic, and a crucial payment-status caveat. Every sentence adds value—there's no fluff or repetition. The structure follows a logical flow that an agent can parse efficiently.

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?

There is no output schema, so the description fully explains the response shape: bill fields, transactions[] when opted in, batch {results, errors}, and the transactions_hint. It also covers error-prone edge cases (open bills, pending lines, payments of previous bills). For a tool with this complexity, the description is extremely complete and leaves no critical ambiguity.

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 explains bill_ids (array, use with list tool), account_id (required for include_transactions), and include_transactions (opt-in, triggers extra scan). However, transactions_detail (an enum with values compact/rich/raw) is not explained in the description, leaving a gap for that parameter. Still, the majority of parameters are well covered, so a 4 is 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 states a specific verb and resource ('Returns bill-level detail for one or more credit card bills by id') and lists the key fields. It clearly distinguishes this from sibling tools like openfinance_list_credit_card_bills (which discovers bill ids) and openfinance_list_transactions (which fetches transactions separately). An agent can tell exactly what this tool does and when it differs.

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 guidance: 'use openfinance_list_credit_card_bills first to discover ids' and 'prefer openfinance_list_credit_card_bills which derives payment_status' for paid status. It explains when to pass account_id and include_transactions, and even provides an alternative method for fetching transactions via openfinance_list_transactions. The when/when-not conditions are explicit and actionable.

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