Compare two periods against the noise

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

Beyond the read-only/idempotent annotations, it discloses the 120-day baseline, the cannot_tell case, today's exclusion, and the statistical caveat that within_noise is not 'no change'. This is substantial behavioral context an agent cannot get from annotations alone.

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 purpose is front-loaded and the prose is dense with useful caveats, but the style is somewhat theatrical and longer than strictly needed. Every substantial claim earns its place, though a tighter version could remove rhetorical flourishes.

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?

For a read-only comparison tool with no output schema, it enumerates possible outcomes, explains insufficient-data behavior, and clarifies date/today semantics. An agent has enough to call the tool correctly and interpret the result.

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% and already documents metric and YYYY-MM-DD inclusive period format. The description adds the 'today is left out' behavior and noise-band concept, but does not add per-parameter details such as period ordering or overlap constraints, so it stays at the high-coverage baseline.

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?

Opens with a precise question—'Is the difference between two periods larger than this metric's own noise?'—and immediately names the only calculation, distinguishing it from the query-style siblings. The description also specifies the three answer values, leaving no ambiguity about what the tool does.

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?

Clear context is given: use this tool to test a period difference against the metric's baseline noise, and the closing sentence explicitly disclaims causal/why explanations. It does not name sibling tools as alternatives, so it stops short of full when-not routing.

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