crux_field_data

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It states the tool is read-only, requires a specific API key, and returns the current 28-day field record with p75s and histograms. It also notes the PageSpeed field block is being discontinued, which is useful context. It doesn't detail error behavior or rate limits, but the read-only and data-scope disclosure is solid.

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 compact paragraph that front-loads the core purpose, then adds the field-vs-lab distinction, the key requirement, and the read-only note. Every sentence earns its place with no 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 is complete for a read-only data-fetching tool: it covers the data source, scope, key requirement, and read-only nature. The output schema exists, so return values are documented elsewhere. Minor gaps like pagination or error handling are not critical for this tool's complexity.

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 description coverage is 100%, so the schema already documents all four parameters. The description adds the key context that origin aggregates every page under it and that metrics can be omitted for all available, but these are largely restatements of the schema descriptions. Baseline 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 tool reads real-user Core Web Vitals from the Chrome UX Report for an origin or URL, with p75s and histograms. It explicitly distinguishes field data from lab tests and names the sibling crux_history as the historical counterpart, making it easy for an agent to select the right tool.

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 explicitly says when to use this tool (for current 28-day field data) and contrasts it with lab tests and the discontinued PageSpeed field block. It also names the sibling crux_history, implying the historical alternative, and states the API key requirement. This is strong routing guidance.

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