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

Annotations already declare the tool as read-only, idempotent, and non-destructive. The description adds valuable behavioral context beyond annotations: it uses a real mainland-China network egress and reports specific metrics (HTTP status, latency, DNS resolution), which is not inferable from annotations alone. No contradiction with annotations.

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 two sentences, front-loaded with the core action, and every word adds value. It efficiently conveys the purpose, the measurement results, and why this tool is unique without any fluff or redundancy.

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?

Given the tool's simple single-parameter interface, explicit output schema, and clear annotations, the description is fully complete. It covers the operational context (mainland-China egress), the question it answers, and the key advantage over alternatives, leaving no important gaps for an AI agent to resolve.

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 schema provides 100% coverage for the single parameter 'url' with a clear description ('Full URL to test, e.g. https://example.com'). The tool description adds minimal extra parameter semantics, only implicitly suggesting that the URL should be a complete URL. This meets the baseline for high schema coverage but doesn't exceed it.

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 verb ('Fetch') and resource ('a URL from a real mainland-China network egress'), clearly differentiating it from general-purpose fetching tools like fetch_page. It also explains the output (HTTP status, latency, China DNS resolution), making the tool's purpose unambiguous.

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 explicitly frames when to use the tool ('Answers "is my site/API usable from China?"') and contrasts it with a VPS abroad, implying this is the only way to get China-specific measurements. It doesn't explicitly name sibling tools as alternatives, but the context is clear enough for an AI agent to select it appropriately.

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