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

The description goes far beyond the readOnlyHint annotation: it discloses that probing is done 'at arm's length on a fixed clock,' that every reading is 'traceable to a retained capture,' and that blocked/rate-limited endpoints are distinguished from unreachable ones so a defended endpoint is never reported as dead. It also states 'Not affiliated with any endpoint graded,' adding independence context. These are meaningful behavioral traits not present in the annotations.

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 compact and information-dense. Each sentence earns its place: the first defines the capability, the second adds method/verifiability, the third explains a key distinction, the fourth adds independence, and the last gives usage timing. It is front-loaded with the core purpose and does not repeat schema or annotation information.

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 read-only probe with one documented parameter, no output schema, and a sibling grader, the description fully equips the agent: what it measures, how it measures, how to interpret blocked/rate-limited, when to call, and what it is not. There is no missing context that would cause an agent to misuse the tool.

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 schema covers the single parameter endpoint_id with a description pointing to the free /coverage list. The tool description adds context about the endpoint being an x402/MPP endpoint, but the schema already references the list. With 100% schema coverage and only one parameter, the description adds marginal value beyond the schema, so a 4 is appropriate rather than 5.

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 opens with a direct, specific question-answer framing: it reports liveness, quote, schema, and speed for a known endpoint. It names the resource (x402/MPP endpoint) and the verb (probe), which differentiates it from grading or paying. It is not a tautology and tells an agent exactly what capability is offered.

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 gives explicit when-to-use guidance: 'Call before paying an unfamiliar endpoint, or to check whether one you already use has repriced or rotated its payTo.' This clearly frames the tool as a pre-payment health check and distinguishes it from sibling probe402_endpoint_grade by not being affiliated with grading. No alternative tool is named, but the context strongly implies this is the readiness/quotation probe rather than the grading probe.

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