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

Annotations only supply readOnlyHint=false, openWorldHint=false, and destructiveHint=false, so the description carries the behavioral burden. It discloses the paid nature, that failed or refused fetches are still billed and signed, that the body is never returned, that no account/API key is needed, and where the payment receipt appears. This is substantial behavioral transparency beyond 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 front-loaded with the core purpose and key constraints, then covers payment mechanics and the receipt location. It is longer than average, and the final feedback sentence is peripheral to tool invocation, but nearly every sentence carries operational information that helps the agent use the paid x402 flow correctly.

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?

There is no output schema, so the description correctly explains what the tool returns: signed attestation fields, never the body. It also explains the unusual billing semantics, the two-call x402 payment protocol, the free read-back via attest_read, and the absence of authentication requirements. For a one-parameter paid tool, this is complete enough for correct 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 100% for the url parameter, so the baseline is 3, but the description adds meaning by clarifying that the URL is fetched from the tool's vantage point, the body is never returned, and connection failures still produce a signed, billed observation. This moves beyond the schema's maximum length and protocol constraint without contradicting it.

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 strong verb and resource: 'we fetch a URL from OUR vantage point and return a signed, timestamped attestation.' It lists concrete outputs (hash, byte count, HTTP status and headers) and explicitly excludes the body. It also distinguishes itself from the sibling attest_read by saying the result can later be read back for free with that tool.

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 clearly explains when to call this tool: to create a paid, signed attestation for a third party. It names attest_read as the read-back alternative and gives a step-by-step payment flow (unpaid call for price, paid call with _meta['x402/payment']). It does not enumerate broader when-not-to-use cases, but the context is strong enough for an agent to select the correct tool.

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