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

Annotations already indicate this is not read-only and not destructive; the description adds that the mutation is scoped to the current user's alert state. It does not disclose idempotency, permissions, or side effects, but for a simple state marker the annotations plus description are adequate.

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?

One sentence, front-loaded with the action, with no filler. The parenthetical clarifies terminology without bloating the definition.

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 one-parameter mutation with annotations and no output schema, the description plus schema are sufficient for an agent to invoke the tool correctly. It could add a note about repeated calls or read-state alternatives, but these are not essential at this complexity.

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?

The single 'id' parameter is fully described in the schema as 'Id of the message.' With 100% schema description coverage, the description need not add parameter detail, and it doesn't.

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 ('Mark'), a resource ('a message'), and the precise state change ('alerted'), with a parenthetical clarifying that alerted means 'shown as an alert' and scoping it to 'the current user.' This distinguishes it from sibling tools like mark_message_read and mark_messages_read_bulk.

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 'to the current user' implies this is for per-user alert state rather than a global or read state, but the description does not explicitly say when to prefer this over mark_message_read, update_message, or other message mutations. Usage context is inferable but not stated.

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