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

Annotations already declare destructiveHint=true and readOnlyHint=false, so mutation is known. The description adds the permission requirement (owner-only, billing scope) and the return value ({overageBilling}), which is valuable context beyond annotations. It doesn't contradict annotations and provides useful operational details.

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 sentences, zero fluff. The action and scope are front-loaded, followed by return value and permission. Every word earns its place; no redundant phrasing.

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 simple boolean setter with one fully described parameter and no output schema, the description covers purpose, scope, permissions, and return value. Nothing an agent needs to call it correctly 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% and the parameter description is rich, covering behavioral nuances (billing past allowance vs. free rate, retroactive billing). The description itself adds no new meaning about the parameter beyond what the schema already provides, so baseline 3 is appropriate.

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 ('turn on or off') and names the exact resource ('project owner's overage billing') and scope ('whole account'), clearly distinguishing it from the read-only sibling get_billing by explicitly mentioning that get_billing reads back the returned setting. This gives an agent an unambiguous understanding of what the tool does.

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?

The description implies when to use it (to change overage billing) and contrasts with get_billing for reading. It also states prerequisites (owner-only, billing scope token). It does not explicitly list alternatives, but the sibling set is large and the purpose is clear enough to avoid confusion.

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