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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint. The description adds useful context: it returns a URL, mentions funding apiPackCredits, and explains a key limitation. It does not contradict annotations and provides extra behavioral detail beyond what's in the annotations.

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 concise sentences, no fluff. The primary purpose is front-loaded, and every sentence adds relevant information (what, why, when to call).

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 read-only tool with an output schema, the description covers purpose, trigger condition, and the only parameter's significance. No missing critical information; the tool is self-contained and appropriate for its simplicity.

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 description coverage is 100%, so the baseline is 3. The description adds value by explaining that the parameter's purpose influences the response field next_generation_credits, giving meaningful context beyond the schema's enum description.

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 clearly states the tool 'Return[s] the Console billing URL so a human can fund apiPackCredits,' specifying both the action and the resource. It differentiates from what the tool is not (Generate-scoped keys cannot create Checkout sessions) and is not a tautology.

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?

Explicitly tells when to call: 'Call this after 402 insufficient_credits.' It also implies the context (when API credits are insufficient) and the constraint that generate-scoped keys can't use Checkout, providing clear usage guidance even without naming sibling tools.

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