crux_history

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

Annotations already indicate read-only, idempotent, and non-destructive behavior. The description adds that it returns data at p75 for specific metrics and a fixed number of periods (25), but does not elaborate on potential rate limits or data freshness. The value added beyond annotations is moderate.

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?

Two sentences: the first states the core purpose and scope, the second connects it to a companion tool. Every word earns its place, with no redundancy. Highly efficient and front-loaded.

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 tool with no output schema, the description omits the return format (e.g., JSON structure) or pagination details. However, given the input schema is comprehensive and the tool has only 4 optional parameters, the description covers the primary usage scenario adequately. A small gap in output transparency.

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 100%, so the description's extra guidance on the mutual exclusivity of url and origin ('Use this OR origin.') adds practical value. It also clarifies that metrics are snake_case CrUX names, which is not fully explicit in the schema. This improves usability beyond the schema alone.

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 returns the last 25 weekly collection periods of Core Web Vitals at p75 for a URL or origin via the Chrome UX Report History API. It distinguishes itself from psi_analyze by adding the trend axis, making its purpose specific and distinct from sibling 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 a direct usage context by stating it complements psi_analyze with a trend axis. It also implies when to use (historical trend) vs. snapshot tools. However, it could explicitly mention not to use it for single-point data or when other siblings like crux_snapshot are more appropriate.

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