List sent messages

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

Annotations already declare readOnly, idempotent, and non-destructive behavior. The description adds meaningful behavioral context beyond annotations: unsent drafts appear with null time, results are newest-first, and each recipient's delivery state is included. This gives the agent a realistic expectation of the response shape.

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, no filler. The core behavior is front-loaded, and the sibling alternative is placed at the end. Every clause earns its place by adding a distinct useful fact.

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 simple read-only list tool with complete schema coverage, annotations, and an output schema, the description is fully sufficient. It covers ordering, null-time edge cases, delivery-state scope, and provides an alternative tool pointer. No critical information is missing.

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 baseline is 3. The description does not add much parameter-specific insight beyond the schema; it mentions newest-first ordering which relates to limit/offset semantics, but the schema already explains these parameters adequately.

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 messages sent by this address'. It also adds essential scope details: includes unsent drafts, newest-first ordering, and per-recipient delivery state. This clearly distinguishes it from the sibling list_messages and delivery_status tools.

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 explicitly directs the agent to use delivery_status for a single message's detail, which is a clear alternative-routing instruction. It does not explicitly contrast with list_messages, but the sent-scope is unambiguous and sufficient for most selection decisions.

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