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

Beyond the readOnly/openWorld hints, it discloses meaningful behavior: 'Answers unrated rather than guessing when the evidence is thin' and 'a url never seen is put in line for a free handshake' reveal non-immediate and abstention semantics. This is exactly the kind of context an agent needs and annotations do not provide.

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?

Three sentences, front-loaded with the return purpose, followed by edge-case behavior and retry guidance. Every sentence adds information; no 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?

For a read-only check with no output schema, it covers the main return content, unknown-URL handling, and coverage scope. The remaining gap is that the method parameter is left semantically unexplained, and no sibling is named as an alternative, though the description is otherwise sufficient for invocation.

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?

Schema coverage is only 33%, so the description must compensate. It clarifies id_or_url ('x402 endpoint or its url') and indirectly relates pay_to via the payTo/charges semantics, but it never explains what the optional method GET/POST means or when to supply pay_to beyond the schema's own description.

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 specific verb and resource: 'Return what has been verified about an x402 endpoint or its url...' and enumerates concrete facts (whether it answers, what it charges, whether the price moved), which clearly distinguishes this from planning/capability siblings. The 'Works for endpoints Teppi does not operate' sentence adds a meaningful coverage distinction.

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?

It provides clear usage context: works even for endpoints Teppi does not operate, and unseen URLs are queued for a free handshake, so 'ask again in an hour' is explicit retry guidance. It does not name sibling tools or give when-not-to-use exclusions, so it stops short of a 5.

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