List messages not seen before

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

The description fully discloses the side-effecting behavior: messages are marked with the AiSeen keyword, while human read/unread state is 'never touched.' It also presents dry_run as a preview mechanism. This goes well beyond the annotations, which only state readOnlyHint=false and destructiveHint=false.

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 sentences deliver the core behavior, the side effect, the read/unread distinction, and the dry_run option without any filler. The most important information is front-loaded, and every sentence earns its place.

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?

The description covers ordering, side effects, and preview behavior, which is enough for an agent to invoke the tool correctly. It does not describe the return format, but with no output schema the lack of explicit return-structure details is a minor gap given the tool's straightforward nature.

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%, and both limit and dry_run are already clearly documented in the schema. The description adds only a brief reminder to use dry_run for previewing, so it does not materially improve parameter understanding beyond the schema.

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 uses a specific verb and resource: 'Returns messages this server has not handed over yet, newest first.' It also explains the distinctive AiSeen-marking behavior, clearly separating this tool from the sibling list_messages and the human read/unread state.

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 implies a polling use case by explaining that marking ensures 'the next call returns only what arrived since,' and it gives a clear dry_run usage instruction. However, it never explicitly states when to choose this tool over alternatives like list_messages, nor does it name exclusions.

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