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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It does disclose one useful fact, 'No browser is launched', which is not obvious from the name alone. However, it does not say whether a network request is made, what the return value looks like, how failures are reported, or what side effects, if any, occur. For a check tool with no output schema, this is a significant gap.

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 very short and well-structured: the action is stated first, and the mechanism caveat is a separate second sentence. Each sentence contributes unique information and there is no filler or redundancy. It is concise to the point of being thin, but the structure itself is clean and front-loaded.

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 no annotations, no output schema, and nine optional parameters, the description is far too sparse. The agent is not told what the tool returns, what 'can be opened' actually measures, which parameter should be supplied, or how this tool differs from the many sibling URL and fetch tools. The only contextual anchor is the 'No browser is launched' note, which is insufficient for safe selection and invocation.

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 has 100% description coverage, so each of the nine parameters is already documented individually. The tool description adds no parameter-level meaning and only focuses on 'url', leaving unclear how the other eight optional parameters relate to the check. Baseline 3 is appropriate because the schema carries the parameter documentation burden.

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 gives a specific verb and object ('check whether a URL can be opened') and adds a useful mechanism note ('No browser is launched'). However, 'can be opened' is ambiguous: it is not clear whether this means HTTP reachability, rendering, or URL syntax validity. The description also does not distinguish this from sibling tools like browser-url-ok, web-fetch, or fetch-status, and the schema exposes many non-URL parameters (city, json, query) that the description does not reconcile.

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 is no guidance on when to use this tool versus alternatives. It never mentions browser-url-ok, fetch-status, web-fetch, or normalize-url, nor does it state what kind of URL or check scenario this tool is for. 'No browser is launched' hints at a lightweight check, but it is not framed as a usage condition or exclusion.

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