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

Annotations already declare readOnlyHint=false and non-idempotent, so the write nature is covered. The description adds meaningful context beyond that: the recipient is derived from the original sender, a NEW message is created rather than editing the old one, and the other side is 'woken' (i.e., notification side effect). It does not cover failure modes or what happens with file_ids.

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 compact clauses with the core behavior front-loaded and the selection hint second; every phrase carries information and nothing is padded.

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 mutation tool with three parameters at 0% schema coverage, no output schema, and no annotation detail on side effects, the description should explain what a2a_task_id refers to and what file_ids does. It leaves an agent guessing about the identifier semantics and attachment behavior before a non-idempotent write.

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, but it names an 'in_reply_to' concept that does not match any parameter (the schema uses a2a_task_id), which risks confusing the caller about which field to populate. 'text' and 'file_ids' receive no explanation at all, leaving the required-vs-optional distinction and attachment behavior undocumented.

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 pairs a specific verb (answer) with a specific resource (a DM you received) and states the threading behavior up front. It also implicitly separates itself from send_dm and generic reply by describing the 'threaded on it' relationship, so an agent can pick it without opening the schema.

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?

'Prefer it when the other side should be woken by a fresh message' gives a clear selection condition for this versus a plain send. It does not name send_dm or state when NOT to use this tool, so the guidance is directional but not exhaustive.

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