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

Annotations already declare readOnlyHint and idempotentHint, but the description still adds genuinely new behavior: a hard result cap, page-number or cursor paging, omission of line items, and a caveat about ISO date parsing regardless of sender format. Only rate limits or ordering guarantees for paging are absent.

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 front-loaded sentences: what it returns, when to use it, then the operational constraints. The parenthetical field list is long but each item maps to actionable filtering/sorting information; only the paging clause is slightly compressed.

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 correctly compensates by enumerating return fields, stating the result cap and paging mechanism, and clarifying what is not returned. An agent can call and interpret this tool without further context.

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 coverage is 100%, so the baseline is 3; the description goes beyond it by explaining that dateFrom/dateTo must be ISO YYYY-MM-DD even when the sender's own format differs, which resolves a real ambiguity the schema doesn't address.

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 (Lists) plus resource (invoice summaries) and an explicit enumeration of the returned fields. It distinguishes itself from get_invoice by noting that identifiers and summaries come from here while line items come from the sibling.

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 concrete when-to-use cases (finding an invoice id, the most recent invoice or client, reviewing drafts/unpaid/overdue) and explicitly routes to get_invoice when line items are needed. The exclusion is stated, not implied.

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