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

Annotations already declare readOnly/idempotent/non-destructive/openWorld=false, so the baseline is covered. The description adds genuinely useful semantics beyond that: rules apply only to new incoming mail, are evaluated in creation order, and the first enabled match wins, plus the SuperMailbox-vs-native distinction.

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?

Three tight sentences, front-loaded with verb+resource. Each sentence earns its place: scope, matching semantics, and the disambiguation from provider filters. No filler.

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 simple one-param read tool with no output schema and full read-only annotations, the description covers identity, scope, and rule-ordering semantics well. It stops short of describing the returned rule shape or whether disabled rules are included, which are minor residual gaps.

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% for the single optional accountId, whose description already states it limits results to one connected mailbox. The description's 'for a connected mailbox' phrasing mirrors the schema without adding new syntax or format detail, so baseline 3 applies.

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+resource ('List SuperMailbox rules') plus scope ('for a connected mailbox'), and explicitly distinguishes these from provider-native filters. It does not explicitly name the create/update/delete rule siblings, but the read intent is unambiguous.

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?

Usage is implied (inspect configured SuperMailbox rules), but there is no explicit when-to-use or when-not-to guidance, nor a pointer to create_mail_rule/update_mail_rule/delete_mail_rule for mutation. Adequate but leaves the agent to infer the workflow.

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