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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is known. The description adds behavioral context: it specifies the return fields (count, limit, next_page_token, messages), explains pagination via next_page_token, and directs to get_agentmail_inbox_message for full bodies. This exceeds the minimal annotation coverage without contradicting it.

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 exceptionally concise: two sentences that front-load the core purpose and return structure, then pivot to sibling routing. Every sentence earns its place, with no redundancy 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?

Given the tool's complexity (12 parameters) and the presence of an output schema, the description is complete: it explains the return format, pagination, how to access full message bodies, and how it differs from related tools. The agent has everything needed to call it correctly without opening the schema.

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 all 12 parameters are already documented with descriptions. The description adds context about pagination (next_page_token) and ordering ('newest first'), which clarifies the meaning of page_token and ascending parameters. However, it doesn't provide additional parameter-specific semantics beyond what the schema already offers, so the baseline of 3 is appropriate.

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 lists messages in one inbox with a specific ordering ('newest first'). It distinguishes itself from siblings by explicitly naming get_agentmail_inbox_messages_search for searching and get_agentmail_inbox_threads for conversation grouping. The verb-resource pairing 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 when-to-use guidance by naming the alternatives and the conditions that select them: 'To search rather than page, use get_agentmail_inbox_messages_search; to group by conversation, get_agentmail_inbox_threads.' It also implies this tool is for paging through messages, giving clear usage context.

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