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

Annotations already establish the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description only needs to add context. It usefully discloses the core assumption that spend ≈ share of voice within the same auction, which is real behavioral/interpretation context. It stops short of noting sensitivity, caveats, or what is returned.

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 short sentences, front-loaded with the actual operation before the assumption. The marketing URL is mild noise that does not help an agent select or invoke the tool, keeping it from a 5.

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 stateless three-input calculator with full schema coverage and safe annotations, the essentials are present. However, with no output schema the description never states what it returns (a single estimated spend figure) or any accuracy caveat, leaving a gap an agent might want when interpreting results.

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% (each of the three parameters is documented, including that competitorSovPct can come from an auction-insights tool), so the schema carries the load and a 3 is the baseline. The description adds the auction-matching assumption but no unit/format nuance 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?

States a specific verb (Estimate) and resource (a competitor's ad spend) plus the input basis (share-of-voice data), so the agent knows exactly what it computes. It does not, however, differentiate itself from near-neighbors like google_search_impression_share_value_estimator or impression_share_opportunity_matrix. Clear but no explicit sibling routing.

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 'use this when…' guidance and no alternative tool is named or excluded. The description hints at the methodology (spend maps to share of voice in the same auction) but says nothing about prerequisites, e.g. that the three inputs must come from the same auction/category, or when another spend tool would be preferable.

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