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

Goes well beyond the annotations: 30-day term with no auto-renewal, the 402 challenge-response protocol, accepted payment headers (X-Credito, PAYMENT-SIGNATURE v2, X-PAYMENT v1), wallet ownership without an account, the `compra` mark preventing double credit debits, and the single-settlement x402 nonce with receipt retention. These are exactly the mutation risks an agent needs and are not derivable from destructiveHint/idempotentHint flags.

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?

Markedly redundant: 'Each purchase lasts 30 days, with no automatic renewal' appears twice verbatim, and the 402-with-price statement is repeated in two separate sentences. The useful payment-protocol details are buried after the duplicated material, hurting front-loading.

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 output schema, the description supplies enough of the protocol (402 response carries price, repeat after payment, receipt handling) for an agent to complete a purchase and recover from errors. It could say more about what a successful response returns to confirm entitlement, but the essential behavior is covered.

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 single `plan` enum is already fully documented in the schema; the description restates the same tier benefits without adding format, default, or validation detail. Baseline 3 applies since the schema carries the parameter meaning.

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 ('Buy a plan') and immediately enumerates the three purchasable tiers with what each grants, so an agent knows exactly what this tool transacts. It is clearly separable from siblings like list_plans, cancel_plan, and get_bundle.

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 conveys the purchase flow (get a 402 with price, then pay and repeat) but never states when to choose this over cancel_plan, list_plans, or api_access_buy, nor any prerequisite such as checking plans first. Usage is implied rather than directed.

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