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

With no annotations, the description carries the full burden and does so well: per-action ACL enforcement, billing behavior ('these calls do not meter; inbound mail later meters inbound_email'), temporary-inbox expiry and purge, and delete purging stored messages. It leaves error behavior, idempotency, and rate limits undisclosed.

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-loads purpose then walks the actions, with zero filler sentences. The action= clauses are dense but each carries distinct information; the only cost is length from enumerating five actions inline.

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 8-parameter, five-action multiplexed tool with no output schema and no annotations, the description covers provisioning, ACLs, lifecycle/expiry, metering, and sibling routing. Gaps remain around pagination semantics for audit and error surface, but an agent has enough to invoke each action 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 description coverage is 100%, so the schema already documents kind, domain, localPart, ttlSeconds, limit, offset, and inboxId with per-action applicability. The description's action= clauses largely restate ACL details already present in the schema, adding little beyond the baseline.

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?

Opens with a specific verb+resource pair ('Create, read, delete, and audit receive-only email inboxes') and then enumerates each action with its exact effect and ACL. The receive-only/no-outbound qualifier and the named siblings make it unmistakable against read_inbox_message or manage_inbox_webhook.

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?

Explicitly routes to the right alternatives: read_inbox_message for mail, manage_inbox_webhook for HTTPS notifications, manage_inbox_blocklist for sender blocks. It also states a prerequisite ('Requires an active plan'), but there is no explicit when-not-to-use guidance or fallback behavior if the plan is inactive.

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