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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is fully covered. The description adds that this is a lookup returning matched segments and coverage, and that it mirrors campaign-start behavior, but does not add richer traits such as latency or scoping limits.

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 compact sentences, front-loaded with the outcome and modes; the parenthetical labels efficiently tie inputs to modes. No filler.

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, idempotent lookup with no output schema, the description usefully describes the return content (segments plus coverage per channel), which compensates for the absent output schema. Remaining gaps are minor.

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 the baseline is 3. The description restates the parameter roles (intent_id, product, audience, geography) and the campaign-vs-profile dichotomy, which the schema already documents, adding no new syntax or constraint details.

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 the resource (audience fit) and its two input modes (campaign intent_id vs. described profile) and states what it returns (audience segments and per-channel coverage). It is a clear noun-phrase statement rather than a crisp verb, but an agent can tell what it produces.

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 explicitly distinguishes the two invocation paths — supply intent_id for an existing campaign, or supply product/audience/geography to describe a profile — and frames it as 'the same check a campaign gets when it starts.' It gives no when-not guidance or named alternatives, but the context is clear.

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