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

No annotations are provided, so the description carries the full burden. It discloses the exact fields returned, implying a read-only list operation. However, it does not mention any limitations, potential pagination, authentication requirements, or error cases. While the nature of a list tool makes some of these less critical, the lack of any behavioral nuance beyond the obvious keeps this at a moderate score.

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?

Two sentences with zero redundancy. The first sentence lists the tool's output, and the second provides cross-tool usage instructions. The most actionable information is front-loaded, and every word earns its place.

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 tool with no parameters and no output schema, the description is quite complete. It enumerates the return fields and explains how to use the id downstream. It lacks mention of edge cases like multiple mailboxes, but for a simple list operation this is adequate. The agent has enough information to call the tool and interpret results.

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 tool has zero parameters, so the schema is empty and coverage is 100%. The description adds no parameter information because none is needed. The baseline for no-parameter tools is 4, and the description's extra context about the return fields does not detract from this.

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's purpose: 'List the user's connected mailboxes' and enumerates the specific fields returned (id, address, display name, provider, can-send flag, last sync). It also distinguishes itself from sibling email tools by explaining how the returned id feeds into email_send and email_list_threads, making the tool's role unmistakable.

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 guidance on how to use the output: 'Use the id as `accountId` in email_send or as `account` in email_list_threads.' This tells the agent when to call this tool (to discover available mailboxes) and how to connect it to other operations. It does not mention when not to use it or alternatives, but for a simple list tool this is sufficient.

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