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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering safety. The description adds value by stating 'Free to call' and enumerating the output content (endpoint, USDC price, input example, charging timing, payment method). No contradiction with annotations, and it enriches understanding of what the tool returns.

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 a single, information-dense sentence. It front-loads the usage condition and then packs relevant details (tools, prices, output elements). While long, every clause adds value, and it is well-structured for quick scanning.

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 there are no input parameters and no output schema, the description fully covers what an agent needs: when to use, what it returns, and that it is free. It leaves no ambiguity about how to invoke the tool (no args needed) or what to expect.

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, so the schema is trivially covered at 100%. The description correctly focuses on output details rather than parameter explanations, which is appropriate. Since there are no params to document, baseline 4 fits perfectly.

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 lists New Runtime's x402 paid tools, specifying the verb 'list' and the resource. It provides specific details about the tools (primary source check, rumour check, research bundle, prior-coverage check) and their attributes, making it unambiguous and distinct from sibling tools that likely handle free operations.

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 says when to use: 'when the free tools left a question open and you can pay per call.' It implies that free tools are the alternative, but does not name specific sibling tools or provide explicit 'when-not' conditions. The guidance is clear enough for an agent to decide, but lacks explicit exclusions.

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