lighthouse

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

The description transparently discloses non-obvious behaviors beyond the annotations: it requires node/npx on PATH, fetches Lighthouse on first use, takes tens of seconds, and does not change the page. These details add real value and are consistent with the idempotentHint and destructiveHint annotations, with the page-unchanged claim clarifying the readOnlyHint=false nuance (external side effects like npx downloads).

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 zero filler: the first states the core action and output, the second adds prerequisites, duration, and side-effect caveat. Information is front-loaded and every clause earns its place.

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 an output schema present, return values need not be explained. The description covers purpose, URL source, prerequisites, runtime, and page safety. The only meaningful gap is the semantics of the 'categories' parameter, which prevents a perfect score but does not undermine overall viability.

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 has no parameter descriptions (0% coverage), so the description must compensate. It clarifies the 'url' parameter via 'current or given URL', but the 'categories' parameter is not mentioned at all, leaving its format (e.g., comma-separated vs array) and exact meaning unstated. This is a notable gap for one of two parameters.

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 ('Run'), a resource ('Lighthouse'), and the output ('return the scores'). It also distinguishes itself from browser-level tools like perf_metrics or trace_start by specifying that it invokes Lighthouse via npx, which clearly separates its purpose.

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 implies usage (for getting Lighthouse audit scores) and provides practical context like needing node/npx and taking tens of seconds. However, it does not explicitly say when to prefer this over sibling tools such as perf_metrics or trace_start, or mention any exclusions/alternatives.

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