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

Annotations already establish read-only, idempotent, open-world, and non-destructive behavior. The description adds valuable behavioral context beyond annotations: it is a static-HTML parse only (no JS/SPA rendering), requires no authentication, and works for any public URL. This gives the agent important expectations about limitations and access requirements.

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 description is two sentences and immediately front-loads the core function ('Fetch clean link-preview metadata'), then lists returns. It adds only two relevant constraints (public URL, static-HTML only) and no filler. Every word earns its place.

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 single-parameter tool with rich annotations, the description is complete: it lists the expected output fields, states the parsing limitation, clarifies authentication requirements (none), and specifies URL accessibility. Even without an output schema, the description gives the agent a full picture of what to expect.

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?

The input schema already covers the single parameter well with 100% coverage, describing it as 'The http(s) URL to unfurl'. The description adds useful semantics by specifying that the URL must be public and that static HTML parsing applies, which clarifies what kinds of URLs will work. This goes slightly beyond the schema's baseline.

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 clearly states the tool fetches link-preview metadata, enumerates the exact fields returned (title, description, image, siteName, favicon, oembed), and specifies the scope: any public URL. This is a specific verb+resource definition that leaves no ambiguity about the tool's purpose.

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?

While no alternative tools are listed, the description provides clear usage context: it works for any public URL, requires no signup or API key, and is limited to static-HTML parsing only. This implies when to use it (for simple preview metadata on public pages) and when not to use it (for JS-rendered or SPA pages), though it does not explicitly name alternatives.

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