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

The annotations already establish that this is a non-read-only, non-destructive, non-idempotent write. The description adds useful behavior beyond that by saying it creates the contact if it does not exist, but it does not explain what happens when the email already exists as a subscriber, nor does it describe subscription status or double opt-in effects beyond what the schema already states.

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 short sentences with the core action front-loaded and no wasted wording. It is appropriately sized for a concise tool summary.

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 7-parameter mutation with a nested custom_fields object and no output schema, the description is too sparse. It omits optional parameter behavior, existing-subscriber handling, and double opt-in requirements, leaving the agent with significant gaps.

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 7 parameters and only 43% schema description coverage, the description should compensate but does not. It mentions only the audience and email in passing and says nothing about first_name, last_name, custom_fields, double_opt_in, or send_confirmation_email semantics.

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 gives a specific verb and resource: adding an email address to an audience, and notes that a missing contact is created. It does not distinguish this operation from close siblings such as bulk-add-contacts-to-audience or update-audience-subscriber.

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 when the tool is relevant by naming the action, but gives no explicit guidance on when to use it versus create-contact, update-audience-subscriber, or bulk-add-contacts-to-audience. No prerequisites or exclusions are stated.

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