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

Annotations already declare readOnlyHint=true, so the description's added value is the note that nothing is matched or reconciled and that results are scoped to a single account. It also flags paged retrieval, though it leaves ordering/pagination depth to the schema. Useful additions without contradicting the annotations.

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 tight sentences: what it lists, what it returns, where to get the id, plus pagination and endpoint. Front-loaded with the core action and no filler.

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, the description compensates by naming the returned fields (date, description, amount, side, reconciled flag, receipt state). Combined with the account-id sourcing hint, read-only semantics, and pagination note, an agent has everything needed to invoke it correctly; the rich 100%-documented schema handles parameters.

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 all 15 parameters (q, side, status, date range, amounts, sort, entry_date_period) are already documented in the schema. The description lists output fields rather than explaining parameter semantics, adding no meaning beyond structured data; baseline 3 applies.

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?

Specific verb (List) + resource (bank-statement lines) with explicit scope ('of ONE bank account') and an enumerated set of returned fields. The parenthetical '(read only; nothing is matched or reconciled)' preempts confusion with reconciliation tools, so an agent can tell what it does without opening the schema.

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?

Gives a concrete prerequisite and routing hint: obtain account_id from billy_list_accounts filtered by is_bank_account=true. It scopes to bank lines rather than postings, but never explicitly states when to prefer a sibling (e.g. billy_list_postings) or when not to use this tool.

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