Get Chrome UX Report Field Data

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

Annotations already declare readOnly, openWorld, idempotent, and non-destructive behavior; the description adds meaningful behavioral context by stating that it returns p75 field metrics or a clear no-data result, and by clarifying real-user field data rather than lab measurements. It does not mention rate limits or auth, but the annotations cover the safety profile.

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?

Four short sentences carry distinct information: purpose, parameter guidance, example, and return behavior. Every sentence earns its place, and the most important scoping guidance is 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 an idempotent, read-only tool with a complete input schema and an output schema, the description covers the key decisions an agent must make: which URL/origin to query, what kind of metrics to expect, and what happens when no data exists. Nothing critical is missing.

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 baseline is 3. The description adds value beyond the schema by explaining when to choose page vs origin, specifically mentioning insufficient traffic, and by giving a concrete mobile LCP/INP example that helps ground the formFactor and metric concepts.

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 opens with a specific verb and resource: get real-user Core Web Vitals from Chrome UX Report. It also explicitly distinguishes itself from Lighthouse lab measurements, which sets it apart from sibling analysis tools without needing to inspect their schemas.

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?

It gives concrete selection guidance for scope: page for one URL, origin for a bare origin when page traffic is insufficient. It also clarifies that this is not Lighthouse lab data, but it does not name a specific sibling tool like pagespeed_analyze_page as the lab alternative, so the routing is clear but not fully explicit.

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