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 mentions 'recent messages' and filtering, but doesn't disclose behavior like pagination, ordering, whether spam is included by default, or what happens when folder is omitted. The description adds some context but leaves significant behavioral gaps.

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 concise sentence that front-loads the core purpose and then adds filtering guidance. It earns its place without redundancy, though it could be slightly more structured.

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 list tool with 4 parameters and no output schema, the description covers the main filtering dimensions but omits important context like default folder behavior, ordering, pagination, and whether outbound messages have folders. It's adequate but not complete.

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 only 25% (only 'limit' has a description). The description adds meaning for 'direction' and 'folder' by explaining their purpose, which compensates partially. However, 'domain' remains undocumented in both schema and description, and the description doesn't clarify defaults or interactions between parameters.

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 clear verb ('list') and resource ('messages for a domain'), and distinguishes sent vs received via direction and inbox vs spam via folder. It doesn't explicitly name a sibling alternative, but the scope is specific enough to differentiate from siblings like get_delivery_events or send_email.

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 gives clear context on when to use the tool: for recent messages on a domain, with direction and folder as filters. It doesn't explicitly state when not to use it or name alternatives, but the filtering guidance is actionable and sufficient for basic selection.

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