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

With no annotations, the description must carry the behavioral burden, and it does disclose two important traits: a single fetch ('Fast one-fetch') and the payment model ('Charged only on success. Price: $0.001 USDC on Base via x402'). However, it says nothing about failure behavior, timeouts, JS-rendered pages, or rate limits, which matter for a paid network fetch.

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 definition is front-loaded with the resource and its output fields, then closes with cost and payment mechanics in a compact sentence. The keyword-list style is dense but each item earns its place as a description of the returned payload; no filler sentences.

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 two-parameter tool with no output schema and no annotations, the description adequately covers what is returned and what it costs. It leaves gaps around error handling and page-type limitations (e.g., JS-heavy sites), which an agent would want before committing to a paid call.

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 description coverage is 100%, so both url and jsonld are already documented in the schema, and the baseline of 3 applies. The description's mention of JSON-LD hints at the jsonld toggle but adds no format or default detail beyond the schema.

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 resource and verb-equivalent: 'URL metadata / link preview' and enumerates the extracted fields (Open Graph, canonical URL, favicon, hreflang, robots, JSON-LD). This is far more specific than the bare tool name 'metadata' and lets an agent tell it apart from siblings like markdown or sitemap, which return content rather than SEO metadata. It stops short of explicitly contrasting with those 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?

Usage is implied by phrases like 'link preview' and 'SEO metadata', which signal the when-to-use case, but there is no explicit statement of when to prefer markdown or sitemap instead, and no exclusions or prerequisites. An agent must infer the choice from context.

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