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

Annotations already declare readOnlyHint=true, so 'Read only' is partly redundant, but the description adds traits the annotations do not cover: 'Paged' discloses pagination behavior and 'GET /postings' reveals the underlying read endpoint. It stops short of describing pagination limits or ordering, so not a 5.

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?

A single dense paragraph that front-loads the resource, then the returned fields, then filtering, then behavior. Every clause carries information with 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 usefully enumerates the return fields (date, text, account, amount, side, currency, voided flag), and covers read-only and paged behavior plus filter dimensions. It is nearly complete, missing only ordering/default-sort or pagination-limit details that an agent might want.

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 eight parameters are fully documented in the schema itself, including formats, ranges, and the next_page hint. The description's 'Filter by account, date or period' maps onto existing params but adds no syntax or format detail beyond them, so the 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?

States a specific verb (List) and resource (ledger postings) and immediately disambiguates the domain with '(the bookkeeping entries)', then enumerates the fields returned. An agent can distinguish this from siblings like billy_list_bank_lines or billy_list_accounts without opening a 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?

It says 'Filter by account, date or period', which implies how the tool is used, but there is no explicit when-to-use/when-not guidance and no mention of an alternative sibling (e.g. when to prefer bank lines over postings). Usage is implied rather than directed.

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