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

Annotations already cover read-only/idempotent safety, and the description adds genuinely new context: the plan expires after 60 minutes, which affects agent timing, and it explains the classification of unsubscribe methods. 'Changes nothing' is somewhat redundant with readOnlyHint but reinforces intent.

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?

Dense, front-loaded description with no wasted filler; the core action leads and the plan_id/expiry handoff follows. Slightly long single paragraph but every clause carries information.

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 a read-only scan tool with a full output schema, the description covers purpose, output shape, safety, and the downstream handoff including plan expiry — everything an agent needs to call it and use the result.

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% with all four parameters documented in the schema (days, limit, inbox, inbox_id), so the schema carries parameter meaning. The description adds no additional parameter syntax or defaults beyond what's already structured.

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?

States a specific verb and resource ('scan recent mail for newsletters and mailing lists'), plus the output shape (grouped by sender, unsubscribe method) so an agent can distinguish it from sibling subscriptions_cleanup at a glance.

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?

Explains the workflow context: returns plan_id and sender_key values 'for subscriptions_cleanup', clearly routing the agent to the follow-up tool. It doesn't spell out explicit when-not conditions or alternative scan tools, but the scan→cleanup pairing is clear.

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