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

Even without annotations, the description discloses key behaviors: it emails a confirmation link, nothing is delivered until click, and the assistant cannot confirm on behalf of the user. This is transparent about the tool's side effects and limitations.

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 concise and well-structured, using two sentences to convey the action, process, and usage constraints. No redundant or verbose language, making it easy for an agent to parse.

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 subscription tool with three parameters and no output schema, the description adequately covers the essential context: the double opt-in mechanism, the prerequisite (user-provided email), and the follow-up action (tell user to check inbox). It is complete for the intended use.

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 provides descriptions for all three parameters (100% coverage), so the baseline is 3. The tool description does not add extra meaning beyond the schema; it only reiterates the email requirement in a usage context. No additional parameter-specific details are provided.

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 states the tool starts a double opt-in newsletter signup for an email address, specifying the verb and resource. It explains the confirmation process, distinguishing it from general subscription tools. This is specific and 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?

The description provides explicit usage instructions: only submit an address the person gave you in this conversation, and tell them to check their inbox. It also states the limitation (cannot confirm on their behalf), giving clear when-to-use and how-to-proceed guidance.

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