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

With no annotations, the description carries the behavioral transparency burden, and it does disclose key behaviors: it follows redirects (final URL), returns limited metadata, and does not return full content. It does not mention timeout, error handling, or whether only HTTP(S) URLs are supported, but the core behavior is well disclosed.

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 short, front-loaded with the core purpose, and efficiently lists outputs and the alternative tool. The repeated 'FREE — FREE:' prefix is redundant and adds noise, so it does not earn a perfect score.

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 simple one-parameter tool, the description covers purpose, key return fields, and the main alternative well. However, the missing input format guidance for q is a significant gap because the agent cannot reliably construct the call without knowing whether q is a URL string, key=value pair, or JSON object.

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?

Although schema coverage is reported as 100%, the only parameter description, 'JSON or key=value input for the tool', is a generic placeholder that does not explain what q should contain. The tool description says 'URL' but never explicitly maps that to q or shows an example, so the agent still lacks the precise invocation syntax.

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 checks whether a public URL is reachable and what it is, with a specific verb and resource. It also enumerates concrete outputs (HTTP status, final URL after redirects, content type, page title), making the tool's purpose unambiguous and distinct from the sibling web_fetch.

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 description explicitly routes the agent to web_fetch when full text and links are needed, which implies free_url_check is for lightweight reachability and metadata checks. This provides an explicit alternative and a clear condition, satisfying the when-to-use vs alternatives requirement.

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