crux_summary

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 does not specify that the tool is read-only, depends on Google's CrUX dataset, or may return null for URLs with insufficient data. The safety profile and potential limitations are not addressed.

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 concise sentence that captures the core purpose. It is front-loaded and efficient, but could be slightly expanded to include key context without becoming verbose.

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 has only two parameters and no output schema, the description is adequate for basic understanding. However, it fails to mention what the output looks like or any constraints (e.g., only available for certain origins). With many siblings, additional context would be beneficial.

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 input schema already provides 100% description coverage for both parameters (url and formFactor). The description adds no additional meaning beyond what is in the schema, so a baseline score of 3 is 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?

The description clearly states the function: retrieving real-world field data from the Chrome User Experience Report for Core Web Vitals. It identifies the specific resource (CrUX) and the data type (field data), which differentiates it from lab-based performance tools. However, it could be more explicit about how it differs from siblings like 'analyze_page_speed'.

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?

No guidance is provided on when to use this tool versus the many sibling tools (e.g., 'analyze_page_speed', 'compare_pages'). The description does not mention prerequisites, such as the need for the URL to have sufficient CrUX data, nor does it contrast with alternatives.

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