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

No annotations are present, so the description carries full behavioral disclosure. It reveals the exact HTTP flow (GET → 402 → retry with PAYMENT-SIGNATURE header), explains settlement logic (charged only if a QR detector decodes), specifies payment method (USDC on Base, no ETH needed), and clearly states the tool does not execute the purchase but only returns the request. This is thorough and non-misleading.

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 organized into clear paragraphs with front-loaded purpose in the first sentence. Every sentence contributes: how to use, when to use, payment mechanics, and critical limitation. It is appropriately sized for the tool's complexity and contains no filler or redundancy.

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?

Despite having no output schema, the description explains exactly what the tool returns (live price and exact request). It covers the full context: prerequisites (wallet, no account), process (HTTP flow), settlement, payment network, and the MCP limitation. For a tool of this complexity, the description is complete and leaves no major operational ambiguity.

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 provides 100% coverage with descriptions for both `url` and `size`, so the baseline is 3. The description adds minimal semantic value beyond the schema: it shows how `url` is used in the HTTP request ('GET https://qart.uk/api/v1/qr?url=...') but does not elaborate on `size` beyond what the schema already states. No additional parameter details are needed.

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+resource: 'buy ONE finished QR artwork' and immediately clarifies that it 'Returns the live price and the exact request to make,' which is distinct from merely purchasing. It also explicitly differentiates from siblings by noting that get_credit_packs and Studio tools require an account or OAuth token, while this tool does not.

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 explicitly states when to use this tool: 'the right tool when you have a wallet but no qart.uk account.' It names alternatives (get_credit_packs, Studio tools) and explains why they are unsuitable. It also clearly states a limitation: 'Cannot be performed through MCP itself' and instructs the user to make the HTTP call externally, providing a complete when/when-not guide.

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