CrUX: weekly trend

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

Beyond the annotations (readOnly, idempotent, non-destructive), the description adds useful behavioral details: a maximum of 25 data points, weekly granularity, and that passing a metric returns a single series. This enriches the agent's understanding without contradicting the annotations.

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 compact and front-loaded, with the core purpose in the first sentence and additional parameter details in the second. Every sentence earns its place, with no redundant or extraneous 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?

Given the presence of an output schema and standard parameters, the description covers the essential aspects: what the tool returns (trend over time), key constraints (25 points), and how to filter by metric. It relies on the 'same rules as crux_record' reference, which is a minor gap but acceptable given sibling tool availability.

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 0%, so the description must compensate. It thoroughly explains the 'metric' parameter with concrete examples, but only references 'same rules as crux_record' for url/origin/form_factor, requiring the agent to consult a sibling tool for full semantics. This is helpful but not fully self-contained.

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's function: 'Weekly Core Web Vitals trend, up to 25 points, for charting or regression checks.' It uses a specific verb (trend) and resource (Core Web Vitals), and distinguishes itself from siblings by focusing on history/trend rather than single records or comparisons.

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 clear context for when to use the tool ('for charting or regression checks') and notes the same filtering rules as crux_record. However, it does not explicitly indicate when NOT to use it or directly compare with crux_compare, leaving some room for interpretation.

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