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

With no annotations, the description carries the full burden. It discloses that it performs live probes, checks specific attributes, and mentions the cost per call ($0.003). It implies a read-only health check without explicitly stating non-destructiveness, but the nature of 'probes' makes side effects unlikely. It does not describe return format or error behavior, but the core behavior is transparent enough.

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 front-loaded with a clear question but the second sentence is a dense run-on that tries to pack too much detail into one breath. It could be broken into clearer, more structured sentences. The cost information is useful but adds to the clutter. It is not overly long but lacks crisp structure.

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 description explains what is probed but never states what the tool returns or how an agent should interpret the result. Since there is no output schema and no annotations, the description should clarify whether it returns a simple boolean, structured metrics, etc. This is a significant gap for an agent deciding if this tool fits the task and how to use the response.

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 input schema is empty, so the baseline for parameter semantics is 4. The description does not need to explain parameters because there are none, and the schema coverage is 100% by virtue of being empty.

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 checks the health of the x402 payment rail via parallel live probes of two specific facilitators. It specifies exactly what is measured (supported kinds, schemes, networks, reachability, HTTP status, latency) and distinguishes itself as a health-check tool, differentiating it from siblings like x402_endpoint_verify or settlement_verify.

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 opening question 'Is the x402 payment rail up right now?' clearly sets the context for when to use it. It implies usage for health monitoring but does not explicitly name alternative tools or exclusion conditions. Since the context is clear and no exclusions are needed, it earns a 4.

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