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

Annotations already declare non-readOnly, openWorld, and non-idempotent, and the description is consistent with them ('Each call adds 30 days'). It adds genuinely new context beyond structure: the payment rail (USDC on Base via x402), the cost model, and the API-key requirement. It stops short of stating reversibility or what happens if payment fails, which would matter for a paid mutation.

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 tight sentences, front-loaded with the core action and price, then the cumulative effect and the prerequisite. Every clause earns its place; nothing is repeated.

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?

With no parameters and no output schema, the description covers what an agent needs: what is bought, for how long, at what cost, via what payment rail, and what credential is required. It could go slightly further on failure/retry behavior for a paid call, but the essentials are present.

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 schema leaves nothing to document and the baseline is 4. The description correctly adds no param details and instead explains the implicit inputs (organization API key, payment).

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+resource combination: buying 30 days of Privi Ledger Pro (unlimited entries) for an organization. It also quantifies the effect of each call ('Each call adds 30 days'), which no sibling like ledger_pricing or ledger_signup duplicates, so an agent can distinguish it immediately.

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?

Conveys an implied use case (upgrade when you want Pro) and a prerequisite ('Requires your organization API key'), but never names when to choose this over ledger_pricing or ledger_signup, nor when not to call it. Usage is inferable rather than stated.

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