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

With no annotations, the description carries the full burden of behavioral disclosure. It discloses one negative behavior ('No browser is launched') but does not explain whether the check involves a network request, whether it is read-only, what 'can be opened' means, or what happens to the many discarded inputs mentioned in the schema. This is insufficient for a tool with zero annotation coverage.

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 concise: two short sentences, no filler, and the key clarification is front-loaded. Both sentences earn their place, and the structure makes the tool's core behavior immediately visible.

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 tool with nine optional parameters, no annotations, and no output schema, this description is not complete enough. It does not explain the tool's return value, what kind of check is performed, how the unrelated schema parameters relate to the URL check, or whether network access is involved. The agent lacks critical context for correct invocation and interpretation.

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?

Schema description coverage is 100%, so the schema already documents all nine parameters with individual descriptions. The tool description adds no parameter-level meaning beyond saying 'URL', and it ignores the other parameters entirely. The baseline of 3 applies because the schema does the heavy lifting, but the description does not compensate for the schema's implied diversity of inputs.

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 is not a tautology and adds a useful clarifying note that no browser is launched. However, it does not differentiate from siblings like normalize-url, fetch-status, or playwright-url-ok, and the input schema's many unrelated parameters make the actual scope somewhat ambiguous.

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?

No guidance is given about when to use this tool versus alternatives such as normalize-url, fetch-status, or playwright-url-ok. 'No browser is launched' is a behavioral note, not a usage rule. The absence of any when-to-use or when-not-to-use language leaves selection entirely to the agent's inference.

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