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

With no annotations, the description carries the full burden. It discloses that no browser is launched, but it does not state whether the tool makes a network request, whether it is read-only, what it returns, or what side effects (if any) occur. The phrase 'can be opened' does not clarify the actual behavior.

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 concise — two sentences, no filler — and front-loads the purpose before the key negative trait. It earns every word, though it is short enough to raise questions about completeness.

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 9 optional parameters, no output schema, and no annotations, this description is incomplete. It does not explain which parameter is the subject of the URL check, what the return value is, or how to distinguish this from browser-url-ok and fetch-status.

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 even without parameter guidance in the description. The description does not add meaning beyond the schema, and the schema's URL parameter says 'normalize or cite' rather than 'check,' but the high coverage prevents a lower score.

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 concrete action — 'Check whether a URL can be opened' — with a resource (URL) and adds the boundary 'No browser is launched,' which distinguishes it from the related sibling browser-url-ok. It stops short of a 5 because it does not define what 'opened' means (syntax validation vs network reachability) and does not explicitly name alternatives.

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 on when to use this tool versus alternatives. The only hint is the negative statement 'No browser is launched,' which weakly suggests it is not for browser-level checks, but it never says when browser-url-ok or fetch-status should be used instead.

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