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

Annotations already declare this is a non-destructive mutation (readOnlyHint=false, destructiveHint=false), so the bar is lower, and the description still adds real behavior: the watermark is monotonic ('only moves forward'), so the call is safe to repeat and cannot regress state. It also scopes the effect per-sender ('counts as read for the sender'), which annotations cannot convey. Auth requirements and error behavior are not covered.

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?

Two tight sentences with the core action front-loaded and no filler. The trailing '(M-07)' token is opaque internal notation that an agent cannot interpret and slightly cuts against clarity.

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 only two required parameters and an output schema present, return values need no explanation, so the definition is close to sufficient. The remaining gap is where conv_key comes from and how this interacts with set_watermark/get_watermark, which matters for a watermark-mutating tool in a large sibling set.

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 0%, so the description must carry parameter meaning. It explains up_to_seq well through the watermark semantics ('everything up to it counts as read'), but conv_key gets no explanation of what it is or where to obtain it, leaving one of two parameters underspecified.

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 ('Mark a conversation read') with the scoping parameter (up to a message seq). It is clearly distinct from read-oriented siblings like list_messages or get_watermark, though it never names the nearest sibling, set_watermark, so differentiation is inferred rather than stated.

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?

There is no explicit when-to-use guidance and no named alternatives. An agent must guess whether this is the right call versus set_watermark, mute_conversation, or leaving the conversation unread; the description gives no conditions or exclusions.

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