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

The description adds meaningful behavioral context beyond the annotations: duplicates change nothing, the free plan limits the list to one address, and the operation returns the whole list. These details are not present in the annotations and materially affect how an agent predicts the tool's effects.

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 front-loaded: the core operation and its semantics appear first, followed by plan limits, return value, and an alternative. Every sentence earns its place without repetition or filler.

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 two-parameter tool with no output schema, the description is complete. It specifies the action, the list semantics, the idempotent duplicate behavior, the free-plan constraint, the return value, and the alternative for replacement, leaving no critical gap for an agent deciding to call it.

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 coverage is 100%, so the input schema already documents both parameters well. The description does not add much parameter-specific meaning beyond the schema, matching the baseline expectation for high schema coverage.

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 states a specific verb and resource: 'Adds one address to the list that receives the email on every submission.' It also clarifies the additive behavior ('keeps the others') and the idempotent duplicate case, making the tool's purpose unmistakable and distinct from siblings like remove_recipient.

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 explicitly tells the agent when not to use this tool: 'To replace the list, pass self_email_notification.recipients to update_form.' It also conveys that the tool is for adding, not replacing, which is key guidance for choosing between add_recipient and update_form.

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