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

The read-only, idempotent, non-destructive behavior is already covered by annotations, and the description adds meaningful behavioral context: newest-first ordering, compact summary output, cursor pagination, default inbox, and full-text query exclusivity. It does not mention error cases or rate limits, but those are not required given the annotation coverage.

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 description is compact and front-loaded; the first sentence states the core purpose and defaults, and each subsequent sentence adds a distinct useful fact (query behavior, return summary, pagination, sibling alternative). No unnecessary words or repetition.

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?

Given an output schema is present, the description does not need to detail return fields, but it still mentions the compact summary. It covers defaults, filters, pagination, exclusivity, and sibling redirects, making it complete for an agent to invoke 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%, and the description adds extra semantic value beyond the schema: 'exact sender address' with an example, 'simple KQL' for query, exclusivity constraints, cursor reuse, and folder defaults. This goes well above the baseline for high schema coverage.

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 opens with a specific action and resource: 'List messages of a folder', and clarifies default sorting and filtering. It explicitly distinguishes itself from siblings by pointing to mail_get_message for full content and mail_senders_summary for a whole-mailbox-by-sender view.

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?

It states when to use the tool and when not to: use it for compact message listing/searching, use mail_get_message for full content, and prefer mail_senders_summary for whole-mailbox-by-sender. It also documents that the query filter is exclusive with the other filters, which is crucial usage guidance.

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