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

With no annotations, the description must carry the behavioral burden, but it only discloses a single negative behavior (no browser launched). It does not state whether a network request is made, whether the check is read-only, whether there are rate limits, or what happens when the URL is unreachable. This leaves the agent guessing about side effects and failure modes.

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 extremely compact—two sentences, with the core check in the first and the key caveat (no browser launched) in the second. It earns its place and avoids fluff, but the terseness is slightly disproportionate to the nine-parameter schema it introduces.

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?

Given nine optional parameters, zero annotations, no output schema, and a large sibling set, a two-sentence description is insufficient. It does not explain the return value, which parameter to supply, whether network access occurs, or when to choose a sibling tool. The tool is only minimally invocable from this description.

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 the schema has 100% per-parameter descriptions, those descriptions are disconnected from the stated purpose: `url` is described as 'HTTPS URL to normalize or cite,' and eight other optional parameters (ref, city, feed, host, json, path, zone, query) appear unrelated and are not explained in relation to this tool. The description does not tell the agent which parameter is relevant or that the others are discarded, so high schema coverage does not translate into usable semantics.

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 verb ('check') and resource ('URL'), and the second sentence 'No browser is launched' distinguishes it from browser-based siblings such as playwright-url-ok. However, 'can be opened' is ambiguous—it does not state whether this is a syntactic validation or a network reachability check—so it is not as sharp as the highest-caliber definitions.

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?

There are no explicit conditions for when to use this tool or when to prefer an alternative. The only hint is 'No browser is launched,' which weakly implies a lightweight/non-rendering check, but the description never names fetch-status, web-fetch, normalize-url, or playwright-url-ok as alternatives. An agent gets no routing help.

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