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

Annotations already cover readOnly/idempotent/non-destructive, so the description is free to add semantics — and it does: the status taxonomy, the crucial warning that missing means unknown rather than zero and that totals exclude it, and the remediation paths. That is meaningful behavior beyond what annotations provide.

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 dense sentences with no filler, and the output shape leads. The first sentence is a list-as-sentence fragment that takes a beat to parse, but nothing is wasted.

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 carries the return-value burden and largely meets it by naming the statuses, the row count, and the per-problem line. It still omits the default time window and what the response looks like at the account vs month level, but nothing critical to invocation is missing.

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 from, to and company are fully documented in the schema. The description adds no parameter-level detail (defaults, window semantics, company scoping), 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?

The description names the resource (per-account month coverage) and enumerates the exact statuses returned, which an agent can distinguish from get_metric or list_accounts. It is telegraphic rather than a clean verb+resource statement, but the intent is unmistakable.

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 implies the diagnostic use case ('Missing means unknown, not zero') and routes to adjacent tools by noting that get_metric reports unknown_reason and that a statement upload or pin_balance can fill a month. It never states explicitly when to reach for this tool over get_metric or list_accounts, so usage is inferred rather than given.

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