Reply to merge request discussion

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

Annotations already indicate readOnlyHint=false (mutation), destructiveHint=false, and idempotentHint=false. The description adds the constraint that the thread must be 'existing', but it does not describe side effects like creating a note, requiring permissions, or failure behavior. Given the annotations cover the safety profile, the description adds minimal extra context, meriting a 3.

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, front-loaded sentence with no redundant text. It conveys the core purpose efficiently.

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 tool is relatively simple with a clear mutation action. However, given the sibling tools and incomplete schema descriptions, the description does not fully guide the agent on when to use it or what parameters mean. An output schema exists, so return values are not needed, but the lack of usage guidance and parameter clarification makes it moderately incomplete.

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 50% (project and merge_request_iid have descriptions, body and discussion_id do not). The description does not mention any parameters or clarify the missing ones. It fails to compensate for the gaps, so the agent must infer the purpose of body and discussion_id from names alone, which is insufficient.

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 uses the specific verb 'reply' and resource 'existing GitLab merge request review thread', which clearly indicates the action. It distinguishes from the sibling tool 'create_merge_request_discussion' by explicitly stating 'existing', implying it is not creating a new thread. However, it does not explicitly contrast with resolve_merge_request_discussion, so it is clear but not fully differentiated.

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 provides no guidance on when to use this tool versus alternatives like create_merge_request_discussion or resolve_merge_request_discussion. There are no prerequisites, permissions, or context given. The only indication is 'existing', which is implicit but not elaborated.

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