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

With no annotations, the description carries the full burden and does disclose key traits: read-only, free (no credit cost), and a bounded result (only the first 20 contacts are returned, with a pointer to paging). It does not cover authorization requirements or behavior for a missing/invalid id, which keeps it from a 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?

Two compact sentences, front-loaded with the resource and its returned fields, then the sibling routing and cost/safety note. Every clause adds information an agent would otherwise have to discover.

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?

No output schema exists, so the description compensates by enumerating the main return fields, stating the 20-contact cap, and pointing to the sibling for full pagination. For a one-parameter read tool that is complete enough to call correctly without surprises.

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?

There is a single required `id` parameter whose schema description already says 'Custom audience id (UUID)' at 100% coverage, so the schema does the work. The description implies the id selects exactly one audience but adds no syntax, format, or lookup guidance beyond what the schema provides.

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 exact resource ('One custom audience') and enumerates the payload an agent will receive (status, counts broken out by email/phone/LinkedIn, enrichment progress, column mapping, first 20 contacts). It also explicitly routes full contact enumeration to `get_custom_audience_contacts`, distinguishing itself from `list_custom_audiences` and the contacts sibling.

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?

The directive 'Page through all contacts with `get_custom_audience_contacts`' is an explicit alternative and condition, so the agent knows to use this tool for the single-audience snapshot and the sibling for full contact lists. No inference is required for the most likely ambiguity.

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