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

With no annotations, the description carries the behavioral burden well: it discloses deduplication keys, silent skipping of duplicates and contact-less records, the return counts, and that no credits are consumed. Missing are permission/auth requirements and whether skipped rows are reported in detail.

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?

Three short, front-loaded clauses with no filler; the limit, dedup rule, and return values each earn their place. Slightly compressed notation ("Returns added / skipped / total_contacts") is terse but 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?

No output schema exists, yet the description summarizes the returned counts, which covers the main post-call concern. Combined with the dedup/skip rules, an agent has enough to invoke and interpret the result; only auth and error behavior are unaddressed.

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 coverage is 50%, so the schema already documents the audience id (UUID) and contacts array. The description adds that email, linkedin_url and phone are the dedup identity fields and that the array is capped, but doesn't clarify how other fields (position, company_name) participate.

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 (append), resource (contacts to a custom audience), and an explicit cap of 5000. This clearly distinguishes it from delete/update contact siblings and from create_custom_audience.

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 word "append" implies adding to an existing audience, which nudges the agent away from create/upload flows, but it never names alternatives such as upload_custom_audience or update_custom_audience_contact, nor states prerequisites like the audience needing to exist.

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