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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false. The description adds useful behavioral context beyond annotations: only domains with inbound enabled are included, results are newest first, and email bodies are omitted. This is valuable for understanding the result shape and scope.

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 three tight sentences with no wasted language. The main scope and ordering constraint are front-loaded, followed by the key relational semantic for in_reply_to_email. Every sentence contributes useful information.

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?

Given an output schema, rich annotations, and 100% schema description coverage, the description provides enough context to call the tool correctly. It covers scope, ordering, body omission, and the reply-listing use case. The only minor gap is that it does not route the agent away from list_emails or toward get_email when full bodies are needed.

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 description coverage is 100%, so the schema already explains limit, cursor, domain, and in_reply_to_email. The description adds meaningful semantic detail for in_reply_to_email, explaining that it identifies the sent email being replied to and how to use it to list replies. It does not add much beyond the schema for limit, cursor, or domain, but the extra relational context is helpful.

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: 'List emails received on domains with inbound enabled.' It also distinguishes the scope by noting 'newest first (bodies left out),' implying it is not a full email-fetch tool like get_email. However, it does not explicitly name sibling tools such as list_emails or get_email, so it stops short of full sibling differentiation.

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 the tool is for listing received emails and gives a specific use case for in_reply_to_email: listing replies to one sent email. It does not state when to use this tool instead of list_emails or get_email, nor does it provide explicit exclusions or alternatives, leaving usage guidance at an implied level.

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