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

Goes well beyond the annotations by disclosing a non-obvious return contract ('a site that is down still returns 200 with up:false and the error'), the failure mode and status code for bad/private URLs, and the per-call price with the x402 payment scheme. Annotations only cover the safety profile; the description carries the operational detail.

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?

Front-loaded with the capability and returned fields, then usage triggers, then edge-case/error/pricing notes. Every clause earns its place and nothing is repeated from the schema or annotations.

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?

With no output schema, the description compensates by naming the return fields and the down-site behavior, plus error and cost semantics. An agent has everything needed to call and interpret this tool correctly.

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 coverage is 100% with a single documented 'url' parameter, so the schema already does the work. The description adds no format, scheme, or constraints beyond the schema's 'http/https' note, making the baseline 3 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?

States a specific verb and resource ('check whether a website is up') and enumerates exactly what is returned: HTTP status, response time, redirect chain, and SSL certificate validity/issuer/expiry. This cleanly separates it from siblings like screenshot_webpage or webpage_to_markdown, which fetch content rather than probe availability.

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?

Gives three concrete triggering scenarios (monitoring, diagnosing a broken link, expiring certificate), which is clear context. It never names an alternative sibling or a when-not-to-use condition, so it falls short of the explicit routing a 5 requires.

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