perf_web_vitals

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

With no annotations provided, the description carries the full burden. It clearly states this is a 'Get' operation returning specific metrics with ratings, indicating a read-only behavior. However, it does not disclose details like whether the data is lab or field based, whether a page load is required, or how errors are handled. More context would improve transparency.

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 a single, tightly packed sentence with no redundant words. It front-loads the action and lists the key outputs immediately, making it highly concise and well-structured.

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 simplicity (no parameters, no output schema), the description adequately specifies what is returned (metrics and ratings). It could mention the exact output format or any preconditions, but for a no-input getter, it is reasonably complete. It does not explain abbreviations, but they are standard web terminology.

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 tool has zero parameters, so the schema already fully covers this aspect. The description adds no parameter semantics because none exist, matching the baseline for a no-parameter tool.

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 uses a specific verb 'Get' and identifies a precise resource: Core Web Vitals with the exact metrics (LCP, CLS, FCP, TTFB) and rating categories (GOOD/NEEDS IMPROVEMENT/POOR). This clearly distinguishes it from sibling tools like perf_metrics or CPU profile 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 implies its use case: when Core Web Vitals are needed. However, it does not explicitly mention when to prefer this over alternative sibling tools such as perf_metrics, nor does it state any exclusions or prerequisites. Guidance is implied but not spelled out.

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