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

Annotations already cover the safe-read profile, yet the description goes well beyond: the 2,000-message truncation limit, the `answerCheck`/`partial` fields, partial entries sorted last, oldest-first ordering with wait days and chase counts, and the exclusion rules for no-reply/self/excluded addresses. This is the kind of operational context an agent cannot get from annotations or schema.

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-loaded with the one-line purpose, and nearly every sentence carries operational weight (reply definition, exclusions, truncation). It is dense and slightly overlong, and the closing draft_reply sentence is a mild cross-sell, but nothing is padding.

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?

With no output schema, the description must describe the return shape and does so thoroughly: what each entry contains, ordering, the wait-day and chase counts, and how partial results are marked and sequenced. An agent could consume the output without further guessing.

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 schema already documents every parameter, its default, and the lookbackDays > olderThanDays rule. The description largely restates those bounds, adding only the semantic interpretation of the two-day window and how excludeAddresses is applied, so the baseline 3 is right.

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 first sentence names a specific verb+resource and, crucially, the direction of the relationship: "Messages the mailbox owner sent that nobody has answered." That framing alone separates it from reply-oriented siblings without needing to name them.

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?

The description establishes the trigger scenario clearly (sent mail with no reply) and implies the value of doing it "in one call," but never names the obvious alternative `owed_replies` nor states when NOT to reach for this tool. Usage is inferable, not explicit.

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