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

With no annotations, the description carries the safety burden and does so well: 'Dry-run' and 'Spends nothing' explicitly declare the operation is free and non-mutating, which is the key risk for a credit-consuming domain. It also discloses the informational payload. It stops short of stating whether it enqueues anything or requires specific permissions, so a 4 rather than 5.

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?

Front-loaded with the core action and the key cost constraint, all in a compact two-clause sentence plus a short imperative. The parenthetical '(1 per contact)' is informative rather than padding. Slightly dense list-of-outputs phrasing keeps it from a perfect 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 single-parameter, no-output-schema, no-annotation tool, the description covers behavior, safety, and returned information sufficiently for correct invocation. Naming `enrich_custom_audience` explicitly as the follow-up would make the routing airtight.

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% and the single `id` parameter is fully documented there as a custom audience UUID. The description adds no parameter-level detail beyond the schema, so the baseline 3 applies.

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+resource ('Dry-run of enrichment') and enumerates exactly what the preview returns: contacts needing enrichment, maximum credits, estimated minutes, balance, and startability. This clearly delineates it from the sibling `enrich_custom_audience`, which actually performs the spending action.

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?

Provides an explicit imperative: 'ALWAYS call first and show the cost to the human.' This tells the agent both when to use it (before enrichment) and what to do with the result (surface cost to the user), leaving no ambiguity about sequencing with `enrich_custom_audience`.

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