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

readOnlyHint=true already establishes safety, and the description adds useful behavioral content by disclosing the report's coverage (targets, API keys, runs in flight, run rate, retention). It does not describe output format or any rate limits, but those are minor for a zero-param read-only report.

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?

Two tightly written sentences front-load the main purpose and then frame the use case. There is mild repetition between 'how much of each ceiling is left' and 'how close am I to its limits,' but it reinforces rather than wastes space.

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?

For a zero-parameter, read-only tool with no output schema, the description supplies enough context: it lists the report's contents and the decisions it supports. Nothing an agent needs in order to select or invoke it 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?

With zero parameters, the schema imposes no parameter-semantics burden and the baseline is 4. The description adds no parameter detail because none exists.

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 uses a specific verb ('Report') and resource ('plan ... and how much of each ceiling is left'), then enumerates the exact dimensions covered. That makes it distinguishable from sibling list/get tools like list_targets or describe_access, which cover individual resources or access rather than account-level plan consumption.

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 gives clear context for use by naming the questions it answers ('which plan am I on' and 'how close am I to its limits'). It does not explicitly exclude alternatives or name a sibling to use instead, so it falls short of a 5.

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