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

With no annotations, the description carries responsibility for behavioral disclosure. It does disclose one meaningful behavior: no browser is launched. However, it does not say whether the tool makes a network request, performs only a local shape check, has side effects, or what the return value represents, leaving important behavioral gaps for an agent.

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?

Two short sentences with no filler. The main purpose and the critical no-browser behavior are front-loaded. 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?

The tool accepts nine optional parameters and has no output schema, yet the description does not explain what result an agent should expect, how URL checking works, or which parameters are relevant to which scenario. The description is too minimal for the tool's actual complexity and leaves critical invocation details unspecified.

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, including notes about values being discarded and what each field is for. The description itself adds no parameter-level semantics beyond the schema, so the baseline 3 is appropriate.

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 states a specific verb and resource: 'Check whether a URL can be opened.' It also adds the key differentiator 'No browser is launched,' which helps distinguish it from browser-url-ok. However, 'can be opened' is ambiguous: it could mean syntactic shape validation, network reachability, or HTTP status checking, so it does not fully clarify the exact nature of the check.

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 'No browser is launched' note implies this is a lightweight alternative to browser-based checks, but the description never explicitly says when to use this tool versus browser-url-ok, fetch-status, domain-shape, or normalize-url. Usage context is only implied, not stated.

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