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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint), so the bar is lower. The description adds 'No browser is launched,' a genuinely useful behavioral trait not present in annotations. However, it doesn't describe other behaviors like whether the tool performs network calls or what the result format looks like, so it remains at a moderate level.

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 exactly two short sentences with no filler. The purpose is front-loaded, and the caveat about not launching a browser is placed second. 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 schema exposes eight parameters, many marked as 'discarded after the shape check,' suggesting the tool serves a broader shape-validation role than the URL-only description implies. There is no output schema, and the description doesn't clarify whether only the 'url' parameter is used or whether multiple parameters can be passed, nor what the return value indicates. This ambiguity leaves the invocation unclear despite the rich schema.

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 provides detailed descriptions for every parameter (e.g., 'Git ref name; discarded after the shape check', 'HTTPS URL to normalize or cite'), giving high schema_description_coverage. The description itself adds no parameter-specific meaning beyond confirming the 'url' property is central, so the baseline of 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 clearly states a specific verb ('Check') and resource ('URL') with an outcome ('can be opened'). The second sentence, 'No browser is launched,' adds a distinguishing detail that separates it from browser-launching alternatives like playwright-url-ok, but it doesn't explicitly name or differentiate from sibling tools such as web-fetch or fetch-status.

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 description provides no guidance on when to use this tool compared to alternatives. It mentions 'No browser is launched,' which hints at a lightweight or non-visual check, but there is no explicit statement of when to choose this over other URL-related tools or any exclusionary conditions.

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