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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safe, side-effect-free nature of the calculation is covered. The description adds that the tool returns two derived figures (pool estimate and required budget), which is mild extra value, but it says nothing about assumptions, rounding, or units for the results.

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 sentences, front-loaded with the core computation before the secondary budget output. The trailing promotional link is the one piece that does not earn its place, but overall it is tight and readable.

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?

With no output schema, the description carries some burden to explain returns; it partially does so by naming the pool estimate and required budget. However, for a five-required-parameter calculator it omits output units, assumptions (e.g. cookie/match modeling), and any differentiation from overlapping sibling calculators, leaving it merely adequate.

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%, so all five parameters are already documented in the schema, which sets the baseline at 3. The description restates visitors, window, match rate, target frequency and implicitly CPM (via 'budget'), but adds no unit conventions, valid ranges, or interpretation guidance beyond the schema.

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 names a specific verb (Estimate) and resource (addressable retargeting pool) and enumerates the driving inputs (monthly visitors, window, match rate) plus a second output (budget for target weekly frequency). It is clear what the tool computes, but it never distinguishes itself from close siblings like lookalike_audience_pool_calculator or channel_saturation_estimator.

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?

There is no statement of when to reach for this tool versus the many other pool/budget calculators in the sibling set, and no prerequisites or exclusions. The only added pointer is a marketing URL for a 'full version', which is not actionable invocation guidance.

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