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

With no annotations, the description carries the full burden. It does add real behavioral context — these are paid endpoints settled in USDC on Base (eip155:8453), and paid MCP tools also accept x402 payment in-band — but says nothing about read-only nature, rate limits, or result size/pagination.

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?

Two short sentences, zero waste, with the core purpose and return content front-loaded ahead of the secondary payment-mechanism note.

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 parameterless list tool with no output schema, the description tells the agent what a row contains (method, URL, price) and the payment context — enough to call it correctly. Only minor gaps remain, such as volume of results or whether the list is static or dynamic.

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 takes zero parameters, so per the baseline a 4 applies. The description cannot and need not explain parameter semantics, and it correctly implies the call is unfiltered.

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?

States a specific verb and resource ('Lists paid x402 endpoints') and immediately names the returned fields (method, URL, USD price). No sibling does anything similar, so no differentiation text is needed for an agent to pick it correctly.

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?

Usage is only implied: an agent can infer this is a discovery call for paid endpoints, but the description never states when to call it (e.g., before calling a paid tool, or to check pricing) nor any alternatives. No exclusions or preconditions are given.

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