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

Annotations carry only the safety profile, and the description adds substantial behavior beyond them: 4xx/5xx are returned as data rather than errors, and the full x402 payment handshake (402 + PAYMENT-REQUIRED, USDC payment, resend with PAYMENT-SIGNATURE header) is disclosed. This payment gating is essential to invoking the tool correctly and would be invisible otherwise.

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 English portion is front-loaded and dense with no waste, stating purpose, return shape, and use cases before the payment blocks. The bracketed payment section is necessary but shifts into another language, slightly reducing at-a-glance readability.

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 enumerates return fields, and it also documents error semantics and the payment flow. For a one-parameter tool this is complete enough to call correctly.

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 single parameter, and the description only restates it ('one public URL', 'public page') without adding syntax or format detail beyond the schema. Baseline 3 is appropriate when the schema does the work.

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 (fetch) and resource (one public URL) and enumerates exactly what is returned: status, title, meta/og description, canonical URL, language, link count, text sample. This is clearly distinguishable from the paid buy_* tools and local utilities (csv-json, diff, regex) among the siblings.

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?

Gives concrete use cases ('link previews, source triage and citation checks') so the agent knows when this applies. It does not name alternative tools or state when not to use it, but the context is clear.

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