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

Beyond readOnlyHint/openWorldHint, it discloses cost ($0.002 USDC per successful call), the payment rails (x402 on Base, Solana or Arc), and that failed calls are not charged — material for an agent budgeting calls. It also discloses an epistemic limitation of the result (advertised-by-header, not observed negotiation), which prevents misreading the output.

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 sentences, front-loaded with what is measured and followed by the caveat and pricing — no filler. Slightly dense and the pricing clause is appended to the technical caveat sentence, but every clause carries decision-relevant 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?

An output schema exists, so return values need not be described; annotations cover the safety profile; the description closes the remaining gaps an agent needs — cost, payment mechanics, and what a negative result actually means.

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?

Only one parameter, and the schema already describes it at 100% coverage ('Domain name such as example.com (required)'). The description adds no format, normalization, or edge-case guidance (scheme, ports, subdomains) beyond the schema, so the baseline 3 applies.

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: reports which newer HTTP protocols (h3, draft/HTTP2 alternatives) a site advertises via the Alt-Svc header, plus max-age. It also preempts the false reading implied by its own name by stating this is not a TLS ALPN negotiation, so an agent can separate it from cipher/ALPN-oriented siblings without opening a schema.

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?

Explicitly frames the interpretive condition: the fetch cannot choose a protocol, so a site that negotiates but sends no Alt-Svc will read as 'not advertised'. That is real when-to-trust guidance, but no alternative tool is named for the case where actual ALPN negotiation is wanted (e.g. the cipher-enumeration sibling).

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