Get Core Web Vitals

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

Annotations indicate readOnlyHint=true and openWorldHint=true, meaning the tool performs a safe, read-only operation. The description adds no new behavioral information beyond the name, but given the annotations already cover the safety and non-mutating nature, the description's transparency is adequate. It does not contradict annotations, and the openWorldHint suggests the tool may reach external websites, which is not disclosed in the description but is implied by the term 'website'. The absence of details about rate limits or external dependencies is minor since the tool is read-only.

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, concise sentence that directly states the tool's purpose. Every word is meaningful; there is no fluff or repetition. It is appropriately front-loaded, with the verb 'Get' immediately clarifying the action. This is a model of 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?

Given the tool's complexity (4 parameters, nested threshold object, output schema present), the description is relatively sparse, but the robust input schema and presence of an output schema reduce the need for extensive description. The description covers the 'what' but not the 'how' or nuances like how thresholds affect evaluation or what 'detailed metrics' entails. With the output schema handling return values and the schema handling parameters, the description is sufficient for a read-only tool, so it slightly exceeds the minimum viable.

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?

The input schema already describes all parameters with reasonable detail (url, device, threshold object with fields, includeDetails). The schema description coverage is 75%, so most parameters are documented. The description does not add any additional meaning beyond what the schema provides; for example, it doesn't explain how thresholds are used or how includeDetails alters the output. With high coverage, the baseline is 3, and the description contributes minimal value.

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 'Get Core Web Vitals metrics for a website' clearly identifies the specific metrics (Core Web Vitals) and the resource (a website), using a precise verb. It is specific enough to distinguish it from generic measures like 'get_performance_score', though it could name a specific competitor (e.g., get_performance_score) to further differentiate. The title and description are aligned, with the description adding 'metrics' to clarify the resource.

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 gives no explicit guidance on when to use this tool versus siblings such as 'get_performance_score' or 'compare_mobile_desktop'. However, the purpose is clear enough that an agent can infer it is for Core Web Vitals (LCP, INP, CLS) specifically, which is a subset of performance. There are no exclusions or alternatives mentioned, so the usage context is implied rather than explicit, warranting a mid-range score.

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