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

Annotations already indicate readOnlyHint=false and destructiveHint=false. The description simply restates the mutation ('Adds a reply') without adding extra behavioral context such as required permissions, ordering, or side effects. It does not contradict 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?

The description is a single, direct sentence with no unnecessary words. It is front-loaded with the essential purpose, making it easy to parse and free of 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?

Given the tool has 5 parameters, 4 required, and no output schema, this one-liner is insufficient. It does not explain what iid or target_type represent, how to obtain discussion_id, or any expectations about the reply content. The schema's minimal descriptions are not supplemented by the description.

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 only 40% of parameters with descriptions (project_id and discussion_id). The description does not explain any parameters; it only vaguely implies that body is the reply content. With low schema coverage, the description should compensate but does not.

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 action ('Adds a reply') and the target ('existing discussion thread'). This distinguishes it from tools that create new threads or list discussions, making it specific and actionable.

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 implies usage for replying to an existing discussion, but it does not explicitly mention when to use this tool versus alternatives like creating a new thread or listing discussions. There are no exclusions or references to sibling tools.

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