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

With no annotations, the description carries the full burden, but it only lists output fields and does not disclose that it likely fetches the URL, failure modes, network/privacy implications, or any rate-limit/auth requirements. It is not misleading, just thin.

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 single sentence is compact and places the core action first, but the leading 'Preview:' repeats the tool name/action and adds no information. It is concise rather than wasteful, but not tightly polished.

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 one-parameter tool this is minimally viable: it identifies the input and the three output fields. However, without annotations or an output schema, it should also clarify failure/error behavior and how it differs from metadata-fetching siblings.

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's 'input' property is described only as 'Input to process,' which is generic. The description adds the critical meaning that the input should be a URL, though it omits format specifics such as whether scheme is required.

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 names a specific verb and resource: 'Preview a URL,' and states the expected output (title, image, description). It does not, however, distinguish this tool from overlapping siblings like x402-og-tags, x402-meta-tags, or x402-web-scrape.

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 intended use is implied by the imperative 'Preview a URL,' but there is no explicit when-to-use guidance, no exclusions, and no mention of alternatives. In a large sibling set, this leaves routing to the agent's inference.

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