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

Annotations declare readOnlyHint=false and destructiveHint=false, so the mutation and safety profile are already known. The description adds the useful prerequisite of where to obtain threadId, but it does not disclose permissions, visibility, rate limits, or what the reply affects beyond creating a message. With annotations covering safety, this is adequate context but not rich behavioral detail.

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?

Three sentences, front-loaded with the core action, followed by usage guidance and the key prerequisite. There is no filler; every sentence contributes directly to correct invocation.

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 three-parameter mutation tool with annotations and no output schema, the description covers purpose, usage context, and how to obtain the required threadId. It omits return behavior or visibility details, but given the tool's simplicity and the annotations, it is largely complete for correct selection and invocation.

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 the baseline is 3. The description adds meaning beyond the schema for threadId by specifying it must come from check_support_replies or the original send_support_message response, which is useful semantic guidance for a required parameter. The other parameters (message, retrievalCode) receive no extra explanation.

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 verb and resource: 'Reply to an existing support thread.' It distinguishes from siblings by naming check_support_replies and send_support_message as sources for the required threadId, so an agent can tell it apart from tools that start or read threads.

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 gives a clear condition for use: 'Use when the operator wants to add information to a thread started earlier,' and specifies that the threadId must come from check_support_replies or the original send_support_message response. However, it does not explicitly state when not to use it or route to an alternative for starting a new thread.

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