Get Performance Metrics

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

With no annotations, the description carries the full burden, and it does disclose the returned metric set (score, LCP, CLS, TBT, FCP, Speed Index, TTI, TTFB with ratings). However it says nothing about cost/latency of the live analysis, failure modes for unreachable URLs, or that it is a read-only fetch.

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 tight sentences with zero filler; the purpose leads and the return contract follows. Every element earns its place, especially since no output schema exists.

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?

Because there is no output schema, enumerating the returned metrics is genuinely useful and largely closes the return-value gap. What remains missing is operational context (expected runtime, error behavior, whether results are cached) for what is likely an expensive live audit.

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%, so url and strategy (including the mobile/desktop enum and mobile default) are already fully documented in the schema. The description adds only 'for a URL' and says nothing about what strategy changes, so baseline 3 is appropriate.

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?

States a specific verb (Get) and resource (Core Web Vitals and key performance metrics) plus the target (a URL), which separates it from sibling diagnostics like get_network_analysis or get_js_analysis. It does not name a sibling it is not, so it stops short of full differentiation.

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?

There is no when-to-use guidance, no prerequisite, and no mention of alternatives such as analyze_url or compare_strategies, which sit right next to it in the toolset. The agent must infer that this is the overall-performance entry point purely from the name.

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