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

Annotations already declare this is a non-destructive, idempotent mutation (readOnlyHint=false, destructiveHint=false, idempotentHint=true), so the description does not need to restate safety. It adds the operational behavior that only the target role's messages are affected and that up_to_id is inclusive, but it does not mention what happens if both parameters are supplied or what the response looks like.

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?

A single compact sentence with zero waste. The verb and resource are front-loaded, and the parameter-selection guidance follows immediately. Every clause 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?

For a simple idempotent mutation with no output schema and annotations that already cover safety traits, the description supplies the essential calling context: when to invoke it and how to choose between the two targeting modes. Minor gaps (mutual exclusivity of message_ids and up_to_id, response behavior) keep it from a 5, but nothing critical for a correct call is missing.

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 50%: role and project_id are documented in the schema, while up_to_id and message_ids have no schema descriptions. The description compensates by explaining that message_ids targets specific messages and up_to_id covers everything up to and including that ID, which is a key semantic not present in the schema. The implied either/or relationship is useful, though mutual exclusivity is not stated outright.

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 states a specific verb and resource (mark a role's messages read) and clarifies the two available scopes (message_ids vs up_to_id). It does not explicitly name or differentiate itself from siblings like read_messages or mark_attention_done, but the purpose is unambiguous.

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 phrase 'once you've dealt with them' gives a clear timing cue for when to call this tool, and the 'message_ids, or up_to_id' clause implies an either/or choice between targeting specific messages or a contiguous range. However, there are no exclusions, prerequisites, or explicit alternatives (e.g., read_messages) to help an agent choose among siblings.

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