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

Annotations only declare it is a non-readonly, non-idempotent, open-world write. The description adds much more: the API key is shown once and must be saved, the mailbox receives mail immediately, a 6-digit verification code is sent to the human and completed via verify, and the account is receive-only until attach_human. This is substantial behavioral context beyond the annotations.

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 purpose and outcome (key + mailbox) are front-loaded, and every sentence conveys a distinct rule (code flow, receive-only mode, invite policy, don't re-register). It is dense as a single paragraph, but there is little filler and each clause earns its place.

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?

Although there is no output schema, the description explains what comes back (a one-time API key and a shared-domain mailbox) and how to proceed afterward. Together with the invite-only and reuse-key caveats, an agent has everything needed to call this tool correctly.

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 100%, so the schema already documents username constraints and agent_name. The description adds value beyond the schema by explaining the semantic role of human_email (it routes the verification code and gates sending, and is mandatory under invitation-only signups).

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 precise verb and resource: it opens an Escouade Mail workspace for an agent and returns an API key plus a mailbox. It also distinguishes the sub-behaviors (with/without human_email) and names the related tools verify and attach_human, so an agent knows exactly what this call produces.

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 when-to-use guidance: use human_email to trigger the 6-digit code flow and open sending; omit it to stay receive-only until attach_human; human_email is required under invite-only signups and must have been invited. It also gives a clear when-NOT-to-use rule: if you already hold a key, reuse it instead of re-registering.

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