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

Annotations cover the safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=false), and the description adds real behavioral detail on top: immediate provisioning, no renewal, keyed retry returning the original purchase, and the write scope required. The only tension is that keyed retries behave idempotently while idempotentHint is false — the description conditions it on client_purchase_key, so this is a nuance rather than a contradiction. It says nothing about failure/refund behavior when max_price_cents is breached.

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 dense sentences with zero filler: what is bought, its lifecycle traits, and the auth prerequisite, front-loaded in that order. Every clause carries distinct information.

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 monetary mutation with no output schema, the definition covers cost control, idempotency, and permissions adequately. The remaining gap is workflow context — it never says that 'offer' comes from get_offers or that 'authorization_id' comes from authorize_credit_spending, both of which are sibling tools an agent would need to complete this call.

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 60%: idempotency_key, max_price_cents, and client_purchase_key already carry descriptions, and the description reinforces the client_purchase_key retry semantics. However, neither schema nor description explains 'offer' (enum of two plan SKUs) or 'authorization_id' — the phrase "with credit" only hints that the latter is a credit authorization handle. 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 gives a specific verb and resource plus scope: "Buy one 30-day prepaid period of a memory plan with credit." It distinguishes itself from siblings such as buy_board_pass and buy_board_post_time by naming the product (memory plan) and duration, so an agent can route correctly without opening a schema.

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 states the key usage facts an agent needs before calling: paid with credit, applies immediately, no auto-renewal, and the required scope 'orders:write'. It does not, however, point at sibling alternatives (e.g., get_offers to obtain the offer, authorize_credit_spending to obtain an authorization) or state when not to use it.

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