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

The description discloses 'No browser is launched,' which is useful behavioral information, but it does not explain what the tool actually does—network request, DNS check, syntax validation, or something else. With no annotations, the full burden is on the description, and it leaves core behavior ambiguous. The schema's 'discarded after the shape check' phrasing suggests a local validation, which the 'can be opened' wording does not convey.

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 front-loads the main idea in the first sentence. The second sentence adds a meaningful behavioral constraint. However, the brevity comes at the cost of accuracy and completeness, so it earns slightly below a perfect score.

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 parameters, no annotations, and no output schema, this one-and-a-half-line description is insufficient. It does not explain what result the agent should expect, whether any side effects occur, or which parameter to use for which goal. The description covers only a narrow URL-focused scenario and leaves the broader tool behavior unexplained.

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 baseline is 3. The description adds no parameter-level meaning beyond the schema, and its exclusive focus on 'URL' may mislead an agent into ignoring the other valid input types. Still, each parameter is already individually documented in the schema.

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 says 'Check whether a URL can be opened,' which is a specific verb and resource, but it only matches one of the nine input params (url). The schema also supports city, feed, json, path, zone, query, and other values, so the stated purpose is misleadingly narrow. 'Can be opened' is also ambiguous and does not differentiate this from sibling tools like browser-url-ok.

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 alternatives such as browser-url-ok, fetch-status, or web-fetch. The only hint, 'No browser is launched,' is a constraint, not an explicit usage guideline.

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