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

Annotations already indicate a non-read-only, non-idempotent, non-destructive write operation. The description adds context beyond annotations by specifying the provenance of required credentials (submission response) and the range of intended follow-up actions, including withdrawing a request. This is useful behavioral context, though it doesn't detail side effects or response behavior.

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 three sentences long, front-loads the core action, and wastes no words. Every sentence earns its place: what it does, when to prefer it, and what inputs are needed. Excellent structure for an AI agent.

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 3-parameter write tool with full schema coverage and a clear purpose, the description is nearly complete. It covers the key prerequisites and the primary decision rule. It doesn't mention return values or error cases, but the absence of an output schema and the simplicity of the operation keep this gap minor. A 4 is appropriate.

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 100%, so each parameter is already documented in the schema. The description adds modest context by explaining that message_id and access_token come from the submission response, but the schema's parameter descriptions already convey this. With full schema coverage, the baseline of 3 is appropriate.

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 action ('Add a follow-up to a thread you opened') on a clear resource, and enumerates concrete purposes (answer, add detail, correct, withdraw). It also differentiates from sending a brand-new message, which maps to the sibling message_human_operator. This is a precise and unambiguous purpose statement.

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 explicitly says to prefer this tool over sending a brand-new message about the same subject, giving an alternative condition and a clear routing rule. It also states the required inputs (message_id and access_token from the submission response), which tells the agent when the tool is usable. This is strong usage guidance.

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