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

Annotations already declare idempotent=true and destructive=false, so safety is largely covered. The description adds that this only sets state and produces no reply, and hints at an auto-ack side effect in reply, but says nothing about whether the sender is notified or how long the 'working' state persists.

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 tightly packed sentences with the core action front-loaded and the sibling note second; no filler.

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?

Annotations plus no output schema cover safety and returns, and the purpose is legible, but the single undocumented parameter with a mismatched-sounding name (a2a_task_id for a DM) is a real gap an agent could stumble on.

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?

With one required parameter at 0% schema coverage, the description carries the full burden and says nothing about it. The name a2a_task_id is especially confusing for a tool that acks an inbox DM, and the description does not explain how to obtain it or what it identifies.

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 an inbox DM as being worked on') and names the state it sets ('working'), which distinguishes it from reply. It is clear without the schema, though the transition it performs (from what prior state) is left implicit.

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?

It gives an explicit usage condition ('without replying yet') and points to the alternative, noting that 'reply acks for you'. It stops short of saying when an ack is required versus optional, but the routing to reply is concrete.

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