Add Subscriber

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

Describes non-throwing behavior for suppressed/invalid addresses, beyond annotations (idempotentHint, destructiveHint). No contradiction with 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?

Two concise sentences, front-loaded with key info, no wasted words.

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?

Covers basic use and outcome, but lacks detail on all 7 parameters and nested merge_fields. Output schema exists, partially compensating.

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?

With only 29% schema description coverage, description adds no parameter details. Does not explain key params like consent_ip, display_name, merge_fields, idempotency_key.

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?

Clearly states verb 'add', resource 'subscriber', target 'audience', and mode 'single opt-in'. Distinguishes from sibling batch tool 'shipmail_add_subscribers_batch'.

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?

Mentions 'single opt-in' and outcome behavior, implying use for individual subscribers. However, no explicit 'when not to use' or direct comparison with batch tool.

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