Run Lighthouse (Core Web Vitals)

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

Even with readOnlyHint and openWorldHint annotations, the description adds rich behavioral detail: runs via npx, reports specific metrics with thresholds, explains the INP/TBT fallback, mentions top speed opportunities, and discloses timing and Chrome requirement. This goes well beyond 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 yet information-dense: it packs purpose, metric details, fallback behavior, timing, and a prerequisite into four efficient sentences without redundancy. Every sentence contributes value.

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?

It explains what the tool reports (scores, Core Web Vitals, speed opportunities) and caveats like slowness and Chrome requirement. However, since there is no output schema, it could be more explicit about the return format (e.g., JSON object, text report) or whether artifacts are saved. Still, the essential usage is well covered.

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 schema already covers both parameters with full descriptions (url and form_factor), so baseline is 3. The description does not add parameter-specific details beyond the schema; it focuses on output and behavior rather than parameter nuances.

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 runs Google Lighthouse for performance and SEO categories, naming specific Core Web Vitals metrics. However, it does not explicitly differentiate from sibling tools like seo_full_audit that also cover SEO, so it lacks explicit sibling distinction.

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 useful context by noting it is 'Slow (~1-2 min)' and 'requires Chrome installed', which implies when it is appropriate to use. It does not explicitly name alternatives or when-not-to-use, but the context gives clear practical guidance.

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