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

Beyond the annotations, the description discloses the key behavior that this call returns immediately without doing provider I/O, making the asynchronous, poll-later contract explicit. The annotations already cover safety and idempotency, so this addition is exactly the context an agent could not infer elsewhere.

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?

Four short sentences, front-loaded with the action and the async contract, then the follow-up sequence, then the caveat about false negatives. Every sentence contributes information that affects how the tool is called.

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 an async enqueue tool with no output schema, the description explains the timing, follow-up calls, and result interpretation well. It stops short of saying what the immediate return value contains, such as a job handle or an acknowledgment, which would have closed the remaining gap.

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 coverage is only 50%: `accountId` has no description, while `rfcMessageId` is documented in the schema. The description partly compensates by stating that RFC IDs stay scoped to `accountId`, which explains why the account must be supplied. It still doesn't say where to obtain `accountId`, such as from `list_mail_accounts`, which leaves a small gap.

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 opens with a specific verb and resource: 'Queue a durable, idempotent RFC Message-ID lookup for background provider resolution.' It clearly distinguishes this from the lookup siblings by making explicit that this only enqueues work, while the actual read is done by `find_cached_thread_by_rfc_message_id`.

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 a full workflow: poll `find_cached_thread_by_rfc_message_id` later, then queue `request_cached_thread_refresh` if a thread is found. It also warns that a negative or not-cached result is not proof that no match exists, which prevents an agent from misreading an empty result.

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