performance_timeline

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

With no annotations, the description carries full burden. It discloses that the tool reads data (non-destructive) and is fast with no trace capture. It does not mention potential failure cases, but the behavioral traits are adequately transparent for a read operation.

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 at two sentences. It front-loads the core action ('Read...') and each sentence adds value: purpose, data source, returned metrics, and performance characteristic. No superfluous text.

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 no parameters and an output schema, the description sufficiently covers what the tool returns and its use case. It could mention scenario limitations (e.g., page not loaded), but for a simple read tool it is complete enough.

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?

There are zero parameters, so baseline 4 applies. The description does not need to add parameter details, and the schema coverage is 100%.

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 reads timing data via the Performance API and lists specific metrics (TTFB, DOMContentLoaded, etc.). It distinguishes itself from siblings like performance_trace_start/stop by noting 'no trace capture' and positioning itself for smoke tests.

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 usage context by stating it is 'best for smoke tests' and implying it is fast. While it doesn't explicitly list when not to use or alternatives, the context is clear enough for an agent to decide.

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