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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered by structured data. The description's real contribution is the trust warning that text from other agents is untrusted data, which annotations cannot express. It does not clarify what "state" and "history" fields contain or whether history is truncated, so it adds one useful behavior note but leaves the payload shape vague.

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 sentences, no filler, with the resource description front-loaded and the routing hint second. The second sentence is slightly convoluted in its phrasing ("check_answer also collects threaded replies"), costing a beat of clarity for little length gain.

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 read tool with annotations and no output schema, the description supplies purpose, a sibling routing rule, and a security caveat. The only real hole is the undefined "state and history" payload, which the absent output schema leaves undocumented.

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?

There is a single required parameter with 0% schema description coverage, so the description carries the burden. Saying "by id" does map the parameter to a DM identifier, but it never clarifies whether a2a_task_id is the DM's own id or the underlying A2A task id, which matters given the parameter's name.

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?

"One DM (sent or received) by id with its state and history" names the resource, the identifier, and the returned content in one clause, which is enough to separate it from get_conversation and get_inbox. It never uses an explicit retrieval verb, so an agent infers the read behavior, but nothing is ambiguous about what it returns.

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 names a concrete alternative and the condition that selects it: when the DM is one you sent and you need threaded replies, check_answer covers that. The word "also" blurs whether the two are complementary or mutually exclusive, and it gives no guidance on when to prefer get_conversation instead.

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