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

With no annotations provided, the description carries the behavioral disclosure burden. It explicitly states 'Read-only, free,' and adds pricing context ('2 credits per contact'). This is strong for a simple read operation, though it doesn't describe response format or error behavior.

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 sentences with no filler. The key details are front-loaded, and every clause adds value: scope, slug, returned fields, and cost calculation.

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 one-parameter read-only tool with no output schema, the description is complete. It names the main return fields (size, description, freshness) and explains the cost-relevant contact count. Enough for an agent to call it correctly and interpret the result.

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?

The input schema already documents the single slug parameter with a helpful note that it is a human-readable slug, not a UUID. The description adds that the slug identifies a 'marketplace set,' which is useful, but the schema already covers the parameter's core meaning, so this is baseline 3.

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 states a specific verb ('Details of one marketplace set'), a specific resource ('by slug'), and names the returned fields (size, description, freshness). This clearly differentiates from siblings like list_audience_sets and get_audience_set_contacts.

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 description gives clear context: use this to view details of a single marketplace audience set and to compute purchase cost from the contact count. It does not explicitly name alternatives or exclusion conditions, but the marketplace-set framing and cost guidance make the intended use apparent.

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