crux_page_vitals

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

With no annotations, the description carries the full burden of behavioral disclosure. It reveals that it requires a CRUX_API_KEY environment variable, returns p75 percentile and ratings, and handles insufficient data with a 'not_enough_data' verdict. It lacks mention of read-only nature, rate limits, or error handling, but covers the essential 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 and well-structured, leading with the core purpose, then detailing return format, edge cases, and prerequisites. Every sentence adds information without 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?

The description covers the tool's purpose, parameters, return format (p75 and ratings), edge case (insufficient data), and prerequisite (API key). With an output schema present, the lack of detailed return structure explanation is acceptable. Minor omissions like rate limits or error codes prevent a perfect score.

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?

Since schema description coverage is 0%, the description compensates by specifying the allowed values for form_factor ('ALL_FORM_FACTORS' | 'PHONE' | 'DESKTOP' | 'TABLET') and noting that url is required. It could further clarify the expected URL format (e.g., fully qualified), but adds significant value beyond the bare schema.

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 clearly states it fetches current Core Web Vitals (LCP, INP, CLS, FCP, TTFB) for a URL from the CrUX API, establishing a specific verb and resource. However, it does not explicitly distinguish itself from the sibling tool 'crux_history,' which likely provides historical data, missing an opportunity for differentiation.

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 no guidance on when to use this tool versus alternatives like 'crux_history' or other analytics tools. It does not mention when not to use it or any prerequisites beyond an API key, failing to help the agent choose appropriately.

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