list_sender_identities

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

Read-only and idempotent behavior is already captured by annotations, so the description adds useful context about what these identities represent: account-owned addresses configured by the operator, not addresses taken from messages. It does not discuss response format or ordering, but an output schema exists.

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?

Three concise sentences: the main purpose comes first, then the integration with draft-saving siblings, then a clarifying exclusion. Every sentence earns its place and there is no redundancy.

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?

With no parameters, an output schema, and strong annotations, there are no material gaps. The description fully explains what the tool returns, why an agent would use it, and how the result relates to the draft tools.

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 parameter baseline is 4. The description still adds semantic value by explaining how the returned identities are used as required or optional values in the save_draft and save_reply_draft tools.

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 a specific action (list) and a specific resource (operator-configured addresses allowed in a draft's From header). It also distinguishes itself from sibling email/message-listing tools by focusing on the server's sender identities rather than message contents.

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 connects the tool's output to save_draft and save_reply_draft: save_draft requires one of these identities, and save_reply_draft accepts one or chooses its own. It does not explicitly contrast with sibling tools, but the intended usage is unmistakable.

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