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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description adds genuinely new behavioral context beyond that: it discloses a bounded cost profile by downloading only 'a small prefix of the page' rather than the full document. It doesn't state rate limits or failure semantics, which keeps it short of 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?

One compact sentence plus a short cost caveat, with the most important information (what is checked) front-loaded. The long enumeration of outputs is dense but each item is actionable for deciding whether to call it.

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?

An output schema exists, so return-value explanation is unnecessary and the description correctly avoids it. For a read-only single-param probe, the remaining gap is sibling routing: it doesn't say when to prefer extract_url or extract_url_structured over this inspection step.

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?

Only one parameter with 100% schema coverage, so the schema already documents the URL constraints (absolute, public, default ports, no credentials, no IP literals). The description reinforces 'public URL' but adds no syntax or format detail beyond the schema, which is the baseline-4 case for a single fully documented param.

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?

Uses a specific verb ('check') and enumerates the concrete outputs: reachability, HTTP status, final URL after redirects, content type, page title, and extraction viability. It hints at the boundary with the extraction siblings ('whether extraction is likely to work') but never names them, so differentiation is implied rather than stated.

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 word 'free' and the extraction-likelihood output strongly imply this is a cheap pre-flight step before extract_url, but there is no explicit when-to-use instruction, no exclusion, and no named alternative. The agent must infer the routing from the 'free, lightweight' framing.

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