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

Annotations already declare readOnlyHint=true, destructiveHint=false, and idempotentHint=true. The description reinforces these with 'Safe, read-only performance diagnostic' and 'No file modifications', and adds the crucial behavioral detail that it performs 'static source code analysis' rather than live browsing. This adds context beyond the annotations without contradicting them.

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 well-structured with clear sections (description, usage, behavioral transparency), front-loads the core purpose, and every sentence carries meaningful information. No redundancy or fluff.

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 a single-parameter, read-only tool with no output schema, the description covers purpose, usage, and safety thoroughly. The only minor gap is that it doesn't explicitly describe what the audit returns (e.g., a report format), but given the sibling tools and the nature of audits, this is a reasonable assumption. Overall, it is sufficiently complete for an agent to call it correctly.

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% (the sole parameter 'target' is clearly documented as a URL or file path). The description does not add additional parameter-specific details, but the baseline of 3 is appropriate since the schema already covers it adequately.

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 states a specific verb ('Identifies') and a specific resource ('code-level Core Web Vitals risks'), enumerating concrete defect types (CLS from images, LCP from formats, render-blocking scripts). This clearly distinguishes it from sibling audit tools (e.g., seo_audit_technical, seo_audit_onpage) by focusing exclusively on performance metrics.

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?

Explicit 'USAGE GUIDELINES' section provides a clear 'Use to' directive and a 'Do NOT use' exclusion, explicitly naming Lighthouse as the alternative for real-time browser benchmarks. This leaves no ambiguity about when to select this tool.

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