Add Subscribers (batch)

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

Annotations already indicate idempotentHint=true and non-destructive behavior. The description adds value by clarifying the single opt-in nature and the per-row response behavior. The description does not contradict annotations.

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?

The description is two sentences, front-loading the main action and key details. Every part is necessary and no word is wasted. It is appropriately sized and structured.

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?

Given the tool has an output schema (implied by context), the description effectively covers the batch limit, opt-in type, and return behavior. For a 3-parameter tool with clear annotations, this is complete and sufficient.

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 67%, with some fields having descriptions. The description adds no additional parameter semantics beyond what the schema provides; it only restates the batch size limit. A baseline of 3 is appropriate as the description does not compensate for the missing parameter descriptions.

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 clearly specifies the verb 'Add', the resource 'subscribers to an audience', the batch limit 'up to 1000', the opt-in type 'single opt-in', and the return behavior 'per-row outcome'. It distinguishes from the sibling tool `shipmail_add_subscriber` by emphasizing the batch nature.

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 implies usage for batch additions but does not explicitly state when to use this tool versus the single subscriber add tool. No prerequisites, exclusions, or context for when not to use are provided. The mention of 'single opt-in' gives some context but no direct guidance.

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