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

With no annotations provided, the description carries the full burden of behavioral disclosure, but it reveals only one trait: no browser is launched. It does not state whether the check makes network requests, what side effects occur, what 'ok' means, or what happens when invalid input is provided. The schema hints that many parameters are 'discarded after the shape check', suggesting a generic validation behavior, but the description does not surface this.

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, both front-loaded and free of filler. The second sentence ('No browser is launched') adds behavioral value and earns its place. It could be considered overly terse given the tool's 9-parameter schema, but as a standalone statement it is well structured and easy to parse.

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 has no annotations, no output schema, and a complex 9-parameter schema, yet the description is only two sentences. It fails to explain the return value, the definition of 'ok', which parameters are relevant, or how this tool differs from sibling URL-related tools. The schema covers parameter descriptions well, but the overall context around invocation, expected output, and edge cases is largely missing.

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 every parameter already has a meaningful description and the baseline is 3. The tool description itself adds no parameter-level semantics; it does not explain which parameter should be used or how the various parameters relate to the URL check. The schema descriptions are informative (e.g., 'Git ref name; discarded after the shape check'), but the description does not clarify how they map to the stated purpose.

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 action ('Check whether a URL can be opened') and adds a useful clarifier ('No browser is launched'), so it avoids tautology. However, the meaning of 'can be opened' is vague—it could refer to syntax validity, DNS resolution, HTTP status, or browser rendering. The description also conflicts with the broad input schema, which includes many non-URL parameters (city, json, zone, query), making the tool's actual scope unclear.

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 about when to use this tool versus its many siblings such as fetch-status, normalize-url, or web-fetch. The description does not mention prerequisites, alternative tools, or conditions that would make this tool the right choice. The only hint is the negated behavior ('No browser is launched'), which implies a lightweight check but does not help an agent decide.

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