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

Annotations mark this as a non-read-only, non-destructive operation. The description adds valuable context beyond annotations: 'Contact routes through Teppek; raw personal details are never exposed' explains privacy behavior, and it clarifies the message recipient. This is useful for an agent to understand side effects and constraints. No contradictions.

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?

The description is two sentences, front-loaded with the primary action and then the usage nuance. Every sentence contributes: the first states what it does, the second covers when/how to use and the privacy aspect. No fluff or redundancy.

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?

The description is sufficient for a simple write operation with two parameters. It explains purpose, usage context, and where to find the required thread_id. Since the tool has an output schema, return values are covered elsewhere. Minor omissions like error behavior or explicit prerequisite ownership are not critical given the clear 'USER'S OWN' statement and annotations.

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 schema covers body with a meaningful description, but thread_id has no schema-level description. The tool description compensates by explaining that thread_id must come from existing conversations, directing the agent to list_conversations/get_conversation. This adds meaning beyond the bare schema, making up for the 50% coverage gap.

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 clearly states the tool's purpose: replying to an existing conversation identified by thread_id, with the message going to the other participant. It also notes both use cases (owner or inquirer following up), which distinguishes it from starting a new conversation (send_message). The phrasing is specific and unambiguous.

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 description explains when to use this tool (replying into an existing conversation) and how to obtain the thread_id via list_conversations or get_conversation. It does not explicitly mention when not to use it or point to alternatives like send_message, but the context is clear enough for an agent to infer appropriate usage.

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