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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=true, so the safety profile is covered. The description adds two pieces of context beyond that: the CrUX data source and the traffic-volume threshold. It omits what happens on low-traffic URLs (empty/null result) and that CrUX aggregates a rolling window, which are the main behavioral surprises for this tool.

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?

A single compact sentence with the key noun phrase front-loaded and the caveat attached rather than buried. It is efficient, though its brevity is close to under-specification rather than disciplined conciseness.

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?

With no output schema, the description should indicate what comes back (e.g. LCP/INP/CLS with percentile buckets), and it does not. Combined with the undocumented form_factor enum and unstated low-traffic failure mode, an agent can form the call but not interpret or troubleshoot the result.

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 carries the full burden, yet it never explains what form the 'url' must take (exact page URL, scheme, trailing slash) or what 'form_factor' does or why ALL is the default. The 'single URL' phrasing implies a per-page scope but adds no operational detail, and 'form_factor' is entirely unmentioned.

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 names the specific resource (real-user Core Web Vitals for a single URL) and the data source (Chrome UX Report), which clearly separates it from the origin-level sibling cwv_get_origin via the word 'single URL'. It stops short of explicitly naming that sibling or explaining the URL-vs-origin distinction, so it is clear but not perfectly disambiguated.

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 parenthetical '(needs enough Chrome traffic)' communicates a real eligibility precondition, which is useful selection context. However, it says nothing about when to prefer cwv_get_origin, cwv_history, or psi_run_audit instead, leaving the choice among siblings to inference.

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