Compare Metrica segments

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

Annotations already declare readOnlyHint=true, but the description adds meaningful behavioral details: the delta is computed server-side with the exact formula (delta = B − A, delta_pct = (B − A) / A × 100), and a positive delta means growth. This goes beyond the annotation's safety profile.

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 and front-loaded: it states the core purpose first, then explains the delta calculation and defaults, and ends with 'Read-only.' Every sentence contributes useful information with no redundancy or fluff.

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?

There is no output schema, but the description explains the return structure: per-metric values for A and B plus absolute and percentage delta. It also covers defaults, read-only nature, and the delta computation. Given the richness of the input schema, this is sufficient for an agent to invoke the tool correctly.

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 coverage is 100%, so the baseline is 3. The description adds extra meaning by explaining the default date range (last 7 days vs prior 7 days), which is not in the schema's parameter descriptions. This helps the agent understand the date parameters without needing to infer defaults.

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 opens with a specific verb and resource: 'Compare two segments/periods (A vs B) for the same metrics and dimensions', clearly distinguishing it from sibling tools like run_report or run_timeseries. It also specifies the endpoint path and the output (per-metric values and deltas).

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?

It clearly states the intended use case—comparing two segments/periods—and explains the default period behavior ('last 7 days (B) vs the prior 7 days (A)'). However, it does not explicitly mention when not to use it or name alternative tools, so it falls short of a 5.

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