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

The description reinforces the destructiveHint annotation with 'SENDS A REAL EMAIL immediately' in caps, emphasizing the irreversible side effect. It also discloses the response format ({ status: 'accepted', message_id }) and the underlying API endpoint, adding value beyond the annotation.

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?

Three concise sentences cover purpose, critical parameters, return shape, and endpoint. Every clause carries information, and the front-loaded 'SENDS A REAL EMAIL' ensures the most important fact is first. No filler or repetition.

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 an 11-parameter tool with no output schema, the description covers the key parameters, the template dynamic data mechanism, the accepted response, and the API endpoint. It lacks details on error handling and rate limits, but the core behavior is well specified.

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 100% schema coverage, the baseline is 3, but the description adds the conditional relationship between template_id and content, and explains how dynamic_template_data feeds template variables. This operational nuance is not explicitly written in the schema descriptions, giving it extra value.

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 immediately states 'SENDS A REAL EMAIL immediately via SendGrid' with a specific verb and resource, clearly distinguishing it from the sibling list/get/add tools. The sentence is direct and unambiguous, leaving no doubt about the tool's function.

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 clear instructions on required parameters ('from_email' and 'to') and the two content paths (subject+content or template_id). While it doesn't explicitly state when not to use it, the purpose and sibling names make the context clear, and it provides the either/or usage pattern.

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