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

No annotations are provided, so the description carries the full load, and it discloses the most consequential trait: the account_key is shown once and unrecoverable. It also reveals the account is not usable until topped up via create_deposit, which is non-obvious. It does not cover whether account creation costs credits, whether accounts can be deleted, or any rate limits.

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?

Front-loaded and readable, but the final sentence restates the earlier sentence almost verbatim ("call create_deposit to add credits, then pass the account_key to create_inbox or send_message" vs. the preceding "top the account up with create_deposit, then pass account_key to create_inbox"). Roughly a third of the text is redundant.

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 annotations, no output schema, and no parameters, the description does the necessary work: what it produces, the one-time visibility of the key, and the required next steps in the workflow. Minor gaps remain around cost and any preconditions for account creation.

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?

Zero parameters, so the baseline is 4. The description still adds value by naming the two values returned (account_key, account_id) and explaining where each is consumed downstream, which the empty schema cannot express.

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?

Specific verb + resource ("Create a prepaid account") plus the concrete artifacts returned (account_key and account_id). It also scopes the tool against siblings by saying it's only needed for longer-lived inboxes or heavy use, which separates it from simply calling create_inbox.

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?

Explicit condition for use ("Only needed for longer-lived inboxes or heavy use") and a concrete follow-up path: create_deposit to add credits, then create_inbox or send_message. It stops short of stating the alternative outright (e.g. "for one-off inboxes, skip this and call create_inbox directly"), leaving that to inference.

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