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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds real context: the window is month-to-date, not a caller-specified range, and the payload is keyed by serverId requiring a join against listServers. It does not state units (currency, hours) or whether idle servers with zero spend are included, which keeps it short of 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?

Three short sentences, front-loaded with the core behavior, then the join instruction, then the alternative. Nothing is redundant and nothing is missing from the sequence an agent would need.

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 describing the return shape — and it does, naming the three per-server metrics. It falls slightly short on units and on whether the list covers all servers or only active ones, but nothing blocks a correct call.

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 and there is no parameter semantics to elaborate. The description correctly avoids inventing inputs and instead tells the agent how to interpret the serverId values in the response.

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 — breaks down this calendar month's spend per server — and enumerates the three returned metrics (cost, compute cost, time awake). It also explicitly distinguishes itself from getBalance, so an agent can tell the aggregation scopes apart without opening either 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 explicit follow-up guidance (resolve each serverId via listServers and name servers by that name) and an explicit routing rule: for totals and balance use getBalance instead. There is no ambiguity about when to pick this tool over its closest alternative.

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