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

With no annotations, the description carries the full burden and does meaningful work: it discloses that no JavaScript is executed (so SPA content will be missing), that the final URL is post-redirect, and that a per-call x402 payment of $0.002 is required. It omits timeouts, rate limits, and what happens on non-HTML content types, which are secondary but relevant for a fetch tool.

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?

Front-loaded with the use case, then input, then output, then a caveat, then an example and price. The long output enumeration is justified because no output schema exists, and every clause carries 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?

With no output schema, the description correctly compensates by listing the returned fields, and it covers input constraints and cost. The remaining gap is routing: nothing tells the agent why to pick this over the similar site_profile or convert_to_markdown 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?

There is one parameter with 100% schema description coverage — the schema already documents the http(s)-only constraint and the 400/not-charged behavior for private addresses. The description only restates the same constraint and adds an example URL, so 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?

The title and first sentence state a specific verb+resource ('what a URL is', 'build a link preview or citation') and enumerate exactly what metadata is extracted, so the agent knows what it gets back. It does not, however, distinguish itself from siblings such as site_profile, domain_lookup, or convert_to_markdown, which sound like overlapping URL-inspection tools.

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?

'Use when an agent needs to know what a URL is before reading it, or to build a link preview or citation' gives a clear triggering context. It stops short of naming alternatives or stating when-not to use it, which matters here because site_profile and convert_to_markdown appear to occupy adjacent territory.

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