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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds the crucial behavioral fact that is nowhere in structured data: a $0.008 USDC per-call cost via x402 on eip155:8453, which materially affects invocation. It omits error/timeout/redirect behavior, keeping it below a 5.

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 purpose, then a dense but useful inventory of return fields and the price. It is a long run-on sentence, but essentially every clause carries information the agent needs; minor deduction for density rather than any wasted sentence.

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?

No output schema exists, so the description must explain return values and does so exhaustively, while also disclosing the payment requirement. An agent has everything needed to decide to call it and to know it costs money.

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?

With one parameter, 0% schema description coverage, and maxLength 2048 only, the description carries the burden. 'Fetches a URL' confirms the url param is the target page, but adds no scheme/format constraints (absolute? http vs https?) or handling for redirects. Adequate but with a real gap.

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 (fetches a URL) and resource (page metadata) and then enumerates exactly what is returned: title, meta description, canonical, OpenGraph, Twitter cards, JSON-LD, favicon, feeds, hreflang, and SEO checklist. That field list makes it unmistakable against siblings like web_extract, web_headers, and web_links without needing to name them.

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 framing 'for link previews and SEO' gives a clear usage context. It stops short of explicit exclusions or naming alternatives (e.g., 'use web_extract for body text'), so it lands at clear-context-no-exclusions rather than full when/when-not guidance.

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