Add a subscriber

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

Annotations already indicate this is a write, idempotent, non-destructive operation. The description adds meaningful context beyond annotations: adding non-opted-in addresses can cause the publication to be marked as spam. This is a useful behavioral warning not available in structured data.

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 short sentences: the first states the action, the second provides essential opt-in guidance. No filler or redundancy; the important caution is placed immediately after the action.

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 simple add operation with one required parameter, a fully documented schema, and annotations covering mutation/idempotence/safety, the description supplies the one missing piece of judgment (opt-in policy). Nothing needed to invoke the tool correctly is absent.

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 100%, so the schema already documents email, publication, and subscription_type clearly. The description does not add parameter-level meaning, so baseline 3 is appropriate.

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?

Description uses a specific verb and resource ('Add an email address to your subscriber list') and clearly identifies the action. It does not need to differentiate from siblings because the add-vs-list distinction is evident from sibling names, and the action itself is unambiguous.

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?

It gives explicit guidance on when adding is appropriate ('Only add people who asked to be added') and a consequence. It does not mention alternative tools for verifying opt-in, but the opt-in condition is a strong usage boundary.

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