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

Annotations already establish this is a safe, read-only, idempotent, non-open-world lookup. The description adds value beyond them by disclosing the actual payload contents — price, pay URL, and guidance text meant for the end user — which tells the agent this is instructional material it can relay to a human, not data it should act on itself.

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?

One sentence, front-loaded with the core question ('how a human buys credits'), then a colon-delimited list of what is returned. The phrasing 'for an agent to use' and 'what to tell your user' is slightly redundant but each clause contributes useful framing.

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 carries the burden of indicating return contents, and it does so by naming price, pay URL, and user-directed messaging. For a simple zero-parameter informational tool this is nearly complete; only the absence of pagination/expiry or currency details is a minor gap.

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 no parameters, so there is nothing for the description to disambiguate; the baseline for zero-parameter tools applies. The description correctly implies no input is needed to retrieve the purchase information.

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 names the concrete outcome — how a human buys credits and obtains a redeem code — and enumerates what the tool returns (price, pay URL, user-facing message). It is distinguishable from 'balance' and 'generate', though it describes the resource as a workflow rather than stating plainly that the tool returns purchase instructions.

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?

Usage is only implied: an agent should call this when a user needs to purchase credits or obtain a redeem code. There is no explicit when-to-use statement, no note on how it relates to 'balance' (checking existing credits) or 'generate' (redeeming), and no exclusions.

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