purchase_tool

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

With no annotations provided, the description carries the transparency burden. It discloses the payment mechanism (x402), the side effect (creator earns DAC), and trial exclusion. However, it omits the two-step payment challenge flow, which is only detailed in the parameter description, so it is not fully transparent on its own.

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 concise and front-loaded: two sentences that cover purpose, payment, and trial exclusion without wasted words. Every sentence earns its place.

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?

Given the tool's moderate complexity and the rich schema that fully documents all four parameters, the description provides sufficient context for an agent to understand the tool's role. It does not explain the return value, but with no output schema and the schema covering the core workflow, the description is adequate though not exhaustive.

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 description coverage is 100%, so the baseline is 3. The description adds no parameter-level meaning, but the schema already provides thorough documentation, especially for payment_signature with its detailed explanation of the x402 challenge flow.

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 the action ('Purchase a tool') and resource ('from the marketplace'), with a specific and unique purpose. It also distinguishes itself from trial tools by noting 'Trial does not cover this route,' which differentiates it from sibling trial-related tools.

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 implies usage context: it is for purchasing tools, not for trial access. It explicitly mentions what is not covered ('Trial does not cover this route'), but does not name alternative tools or provide explicit when-to-use vs. when-not-to-use guidance beyond that.

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