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

Annotations already provide idempotentHint=true and destructiveHint=false, but the description adds the specific state change (marking as read) and the negative guarantee of not sending a message. This adds useful context beyond the structured annotations and does not contradict them.

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 definition is two short sentences with the core purpose front-loaded and the clarifying negative right after. Every word earns its place; there is no fluff 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?

For a simple, idempotent acknowledgment operation, the description is essentially complete: action, negative guarantee, and required parameter are all clear. Return behavior is not described and there is no output schema, but that is unlikely to prevent correct invocation.

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 the property descriptions for token and message_ids are self-sufficient. The tool description itself does not add parameter-level detail, so the baseline score of 3 is appropriate.

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 'Mark messages as read,' a specific verb plus resource, and immediately adds 'Does not send a new chat message,' which distinguishes it from communication siblings like send_message and send_and_wait. This makes the tool's purpose unmistakable.

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?

'Mark messages as read' clearly states the intended use, and 'Does not send a new chat message' provides an explicit when-not for reply tools. It does not name the alternative tool directly, so the guidance is clear but not as explicit as a full routing recommendation.

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