compare_performance

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

No annotations exist, so the description must carry the full burden. It effectively communicates that this is a read-only comparison tool showing deltas and winners. However, it lacks details on data freshness, caching, or prerequisites (e.g., CrUX data availability), which would have raised the score.

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 well-structured sentences. The first sentence defines the action and scope, the second specifies the output format. Every word is necessary, and the description is front-loaded with critical information.

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 moderate complexity and absence of output schema and annotations, the description covers the core functionality well but omits details like the specific metrics (LCP, FID, CLS), data source, and whether it works for any URL or only those with CrUX data. These gaps reduce completeness.

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%, and the description adds value by explaining the behavior when urlB is omitted (compares urlA mobile vs desktop) and the default device. This goes beyond the schema's parameter descriptions, providing practical usage instructions.

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 the tool compares Core Web Vitals between two URLs or the same URL on different devices, with a specific output of per-metric deltas and winner indicators. It distinguishes itself from siblings like analyze_performance, which likely handles single URLs.

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 clear use cases: comparing two URLs or the same URL across devices. It explains the fallback when urlB is omitted, giving implicit guidance on when to include it. While it doesn't explicitly name alternatives, the sibling tools provide context for when not to use this tool.

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