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

Annotations already cover the safety profile (readOnlyHint=true, idempotentHint=true, destructiveHint=false). The description adds valuable context beyond the annotations by detailing the exact return shape (total load time, HTTP status, phase-by-phase breakdown, content preview) and disclosing a monetary cost of $0.01 USDC via x402.

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 four sentences, each earning its place: core action, return value breakdown, applicable use cases, and cost. The most important information is front-loaded, and there is no redundant or filler text.

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 two-parameter tool with a comprehensive schema and robust annotations, the description covers purpose, output shape, use cases, and cost. The only minor omission is explicit handling of edge cases like unreachable URLs or non-200 responses, but the provided detail is sufficient for an agent to select and invoke the 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 description coverage is 100%, with both url and origin fully documented including default values and the origin enum. The description's phrases 'any URL' and 'chosen global location' merely restate the parameters without adding syntax, defaults, or format details beyond what the schema already provides, so the baseline score of 3 applies.

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 and resource: 'Measure real-world page load performance (response time) for any URL from a chosen global location.' It also enumerates the returned data and mentions use cases. No sibling tool covers latency or performance measurement, so it is clearly differentiated from the other interzoid tools.

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 clear usage context via 'Useful for global latency monitoring, CDN validation, and uptime/performance checks,' which tells an agent when to use it. It does not explicitly name an alternative or describe when not to use it, but since no sibling covers this domain, the guidance is sufficient without exclusions.

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