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

Annotations already establish the write, non-idempotent, non-destructive profile. The description adds the key side effect that it acks the task before submitting, and clarifies recipient scope to the sender only, which is valuable behavioral context beyond the annotations.

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 sentences, zero waste, front-loading the core action and then the sibling routing rule. 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 two-parameter reply tool with annotations covering safety and no output schema to explain, the description covers purpose, side effects, recipient scope, and the alternative tool. Nothing essential 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 0%, so the description must compensate. It does by assigning clear roles: task_id identifies the inbox DM to reply to, and text is the reply content. It still omits task_id format or text constraints, but the semantics are meaningfully clarified.

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?

States a specific verb (reply), resource (inbox DM), and lookup key (task_id), then explicitly distinguishes this from send_dm for group replies. An agent can select 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?

Gives the exact condition for this tool (reply to an inbox DM) and an explicit alternative for a different case (to answer a whole group, use send_dm to the group_id instead). The routing is unambiguous.

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