perf_metrics

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

No annotations are provided, so the description carries the full burden. It discloses that the tool returns current runtime metrics and gives examples, but it does not specify the output structure, confirm that it is a read-only snapshot, or mention any prerequisites like an active CDP session. The word 'current' implies a snapshot state, but behavioral traits are not fully disclosed.

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 a single sentence that leads with the action and object, then parenthesizes relevant examples. It is concise, front-loaded, and every word earns its place, with no filler or repetition.

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?

The tool is simple with no parameters and no output schema. The description covers the main function and lists several metric types, but it omits the exact return format (e.g., JSON object keys) and uses 'etc.' to imply additional metrics. For a zero-param tool, this is reasonably complete, though not fully detailed.

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?

This tool has zero parameters, so there is no parameter schema to clarify. The description correctly implies that no inputs are needed. According to the rubric, a tool with 0 parameters receives a baseline of 4, and the description does not need to add parameter-specific semantics.

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 uses the verb 'Get' with a specific resource ('current runtime performance metrics') and enumerates examples (DOM nodes, event listeners, layout counts, JS heap) that clearly distinguish it from sibling tools like perf_web_vitals or perf_cpu_profile_start. This is specific and unambiguous.

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 no explicit guidance on when to use this tool versus alternatives like perf_web_vitals or perf_cpu_profile_start. The context of 'runtime performance metrics' is clear, but there are no exclusions or references to alternatives, so the agent must infer usage from the name and examples.

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