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

Annotations already cover read-only, idempotent and non-destructive semantics, and the description adds genuinely new behavioral detail: result ordering, the meaning of the 'pending' status, and the fact that deleted servers vanish. Minor omissions only (no mention of pagination or result-size limits).

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 short sentences, front-loaded with what the tool returns, then the status meaning, then the join instruction. Every sentence carries distinct information with no repetition.

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 carries the burden of explaining return values, and it does cover ordering, per-server cost, status meaning, and missing servers. It leaves some field-level detail unspecified, but an agent can call this zero-param tool confidently.

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?

The tool takes zero parameters, so the baseline is 4. The description instead documents output field semantics (status, serverId), which is useful but not required for parameter semantics.

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 and resource ('Lists past calendar months' bills') plus ordering ('newest first') and shape ('cost per server'), so the agent knows exactly what comes back. It does not explicitly distinguish itself from the similar-looking sibling getMonthSpending, which is the main remaining gap.

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 clear usage context – past months, historical view – and a concrete follow-up workflow ('Match each serverId to a name with listServers'). It stops short of naming an alternative such as getMonthSpending or stating 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.