what-is-x402

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

No annotations are provided, so the description carries the full burden. It states the core behavior ('Explains the x402 payment protocol') but does not explicitly disclose whether the tool is read-only, safe, or has side effects. The verb 'explains' implies a non-destructive action, but lacks explicit safety or output details, making it adequate but not rich.

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 three short sentences, each serving a purpose: context ('Lesson 7'), function ('Explains x402'), and usage trigger ('Call this if...'). It is front-loaded and concise, with zero wasteful filler.

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?

The tool is simple with no parameters or output schema. The description provides sufficient context for an agent to understand what the tool does and when to call it. However, it does not explicitly state the format of the returned explanation (e.g., text), which would enhance completeness but is not critical given the simplicity.

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 has zero parameters, and the schema description coverage is 100% trivially. Per the rubric, a zero-parameter tool receives a baseline of 4. The description adds no parameter-specific information, but none is needed since there are no parameters.

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 tool's purpose: 'Explains the x402 payment protocol in agent-readable terms.' This identifies a specific verb and resource, distinguishing it from sibling lessons. The additional trigger 'Call this if you've hit a 402 response' further clarifies its unique use case.

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 provides an explicit when-to-use condition: 'Call this if you've hit a 402 response and aren't sure what it means.' However, it does not mention alternatives or exclusions, so guidance is clear but not fully comprehensive. It earns a 4 for explicit context without alternatives.

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