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

With readOnlyHint=false, the annotations already indicate this is a mutating operation. The description adds no further behavioral details, such as whether creating a sender will fail if the domain is unverified, or what side effects occur. It does not contradict annotations, but it provides no value beyond the structured metadata.

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 a single sentence of four words, making it extremely concise and front-loaded. However, it is so terse that it sacrifices informative content, though it avoids redundancy with the schema. It earns its place by stating the core action, but it could include a brief elaboration without becoming bloated.

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?

Despite having an output schema and a complete input schema, the description omits important contextual information such as prerequisites, limitations, or how the created sender integrates with other email operations. An agent would need to consult documentation or infer behavior from sibling tools like verify_email_domain and set_default_email_sender. This is inadequate for a create operation with multiple optional postal fields that have legal implications.

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 provides complete descriptions for all 8 parameters (100% coverage), including enums and supplementary details like anti-spam law requirements for address fields. The description adds no parameter-specific meaning, so it maintains the baseline score of 3 expected when schema descriptions are comprehensive.

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 the verb 'create' and the resource 'From sender', which clearly identifies the action as creating a sender entity. However, it does not explain what a 'From' sender is or differentiate it from related sender operations beyond the create verb. The phrase is a slight elaboration on the title but lacks specific context about the sender's role in email delivery.

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 no guidance on when to use this tool versus alternatives like update_email_sender, set_default_email_sender, or delete_email_sender. There is no mention of prerequisites such as domain verification or how this sender will be used in future email sends. An agent must infer usage context from the tool name and sibling tools.

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