crux_snapshot

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

Annotations already mark it as readOnly, idempotent, and non-destructive. The description adds valuable behavioral context: it returns a specific 28-day snapshot, uses p75 percentiles, and outputs per-metric categories plus an overall verdict. It also clarifies that no_data is a legitimate response for small sites, which is helpful.

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 with no fluff. Front-loads the core action and key details (metrics, time range, API). Every sentence adds value and the structure is highly efficient.

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 no output schema, the description adequately explains the return value (metrics, categories, overall verdict) and the possibility of no_data. It also mentions the underlying API. For a simple read tool with 3 well-described params, this is sufficiently complete.

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% with good descriptions on each parameter. The description adds that url and origin are mutually exclusive alternatives, which is already implied in the schema descriptions. It does not significantly enhance parameter understanding beyond what the schema provides, so 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 it returns the current 28-day p75 Core Web Vitals snapshot for a URL or origin, listing exact metrics (LCP, INP, CLS, FCP, TTFB) and their categories. It distinguishes itself from the sibling tool crux_history by noting the difference between snapshot and trend.

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?

Explicitly directs to use crux_history for 25-week trends and explains that small pages/origins may return no_data, setting appropriate expectations. This provides clear guidance on when to use this tool versus alternatives.

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