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

Goes well beyond the readOnlyHint/openWorldHint annotations by disclosing redirect-following, the exact per-call price ($0.002 USDC on Base), the x402 payment flow, and the concrete failure mode (unpaid calls return PaymentRequired). This is exactly the context an agent needs before calling a paid endpoint.

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, both dense with information: what is returned first, then payment mechanics. Zero filler and no redundancy with the schema.

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, and the description compensates by listing the return fields explicitly. Redirect behavior and the payment prerequisite are both covered, so an agent has everything needed to call it 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?

Only one parameter and the schema already documents it at 100% coverage ('Public http(s) URL (scheme optional)'). The description adds no syntax, normalization, or size limits for the URL, so it is at the baseline for high schema coverage.

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?

Names a specific resource (URL) and enumerates exactly what is returned: title, description, canonical, language, OG/Twitter cards, favicon, feeds, JSON-LD. This distinguishes it from siblings like url_check (availability) and url_to_markdown (content extraction).

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 'link preview and SEO metadata' framing makes the use case clear, and the pricing sentence gives an agent a reason to weigh the call's cost against alternatives. There is no explicit statement of when to prefer url_links or url_to_markdown instead, 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.