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

Annotations only declare the generic non-read-only, non-destructive, non-idempotent profile; the description adds real value by disclosing the money-spend semantics, the required 'orders:write' scope, the $1 minimum, and that no entitlement results. It omits what happens when max_price_cents is exceeded or how the optional idempotency key interacts with the declared idempotentHint=false, which is a notable gap for a payment tool.

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?

Four short sentences, front-loaded with the action and the amount constraint, with no filler. The fragments ('No entitlement.') are terse but each carries a distinct constraint.

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 real-money mutation with no output schema and only partial parameter documentation, the description should explain the authorization flow, the max_price_cents behavior, and the result of a call. It covers the safety essentials but leaves enough operational detail missing that an agent may still need to inspect sibling tools.

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 33%, and the description only clarifies two of six parameters indirectly: amount_cents (via the $1 minimum) and the authorization/confirmation pair. It says nothing about max_price_cents, client_purchase_key, or idempotency_key, so it does not compensate for the low coverage.

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 states a specific verb and resource: voluntarily spending prepaid credit to support agent operations, with a concrete $1 floor. It also distinguishes the resource from siblings like buy_board_pass or buy_plan_period via the 'No entitlement' clause, though it never names those siblings explicitly.

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 says the call requires 'explicit separate offer authorization and confirmation,' which implies a prerequisite flow via authorize_credit_spending or get_offers, but the required prior tool is never named. 'No entitlement' hints at when this is preferable to a purchase that grants something, yet no explicit when-not guidance is given.

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