crux_history

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

No annotations are provided, so the description carries the burden. It discloses the return format (p75 per week, oldest to newest), the metrics available, and the API key requirement. However, it does not mention rate limits, error handling, or behavior for URLs with no data.

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 with three focused sentences. The first sentence states the core purpose, the second details parameter options, and the third mentions return format and requirement. No redundant information.

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 key aspects: what data is returned (p75 per week), the parameters, and the environment variable requirement. An output schema exists but is not shown; the description provides sufficient context for an agent to use 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 coverage is 0%, so the description must compensate. It explains form_factor options (ALL_FORM_FACTORS, PHONE, DESKTOP, TABLET) and lists metric values explicitly. The url parameter is not described beyond being a string, but the overall parameter meaning is clear from the tool's purpose.

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 'Fetch 40 weeks of Core Web Vitals history for a URL from the CrUX History API.' It specifies the action (fetch), the resource (Core Web Vitals history), and the scope (40 weeks), distinguishing it from siblings like crux_page_vitals.

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 explains parameter options (form_factor, metric) and the required environment variable CRUX_API_KEY. However, it does not explicitly state when to use this tool instead of alternatives such as crux_page_vitals or other analytics tools.

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