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

With no annotations, the description discloses that the tool is anonymous, acts as a price list, and that pack prices can change. However, it doesn't detail response shape or error behavior, though that's less critical for a simple list.

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?

The description is front-loaded with the core purpose, then appends operational guidance about purchasing. While slightly longer than strictly necessary, the extra context is valuable.

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 zero-parameter tool with no output schema, the description provides complete context: what it returns, that it's anonymous, and even next-step actions for purchasing. It fully equips an agent to use the tool and act on its results.

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 input schema has zero parameters, so description is not required to explain parameters. It adds meaning by describing the content of the returned list.

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 clearly states that the tool lists Studio credit packs, their USD prices, and approximate image yields. This explicitly distinguishes it from sibling tools like buy_qr_outright by establishing it as a price list resource.

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?

Explicitly instructs agents to consult this list rather than recalling prices from memory, and distinguishes between self-service top-up (POST /api/qart/x402/credits) and human-only Stripe checkout. This provides clear when/alternatives guidance.

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