add_merge_request_diff_comment

WHAT IT DOES

What add_merge_request_diff_comment does on GitLab MR MCP

AI agents use add_merge_request_diff_comment to create or update resources in GitLab MR MCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your GitLab MR MCP environment.

WHY IT NEEDS A POLICY

Why add_merge_request_diff_comment needs a policy

This tool creates new content (a comment) in a GitLab merge request, which is a reversible modification. It does not delete data (Destructive), execute arbitrary code (Execute), move money (Financial), or merely read data (Read).

From the tool's definition The tool name and description indicate it "Add[s] a comment" on a merge request diff. This creates new data (a comment) in the repository system that is reversible (comments can be edited or deleted).

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

add_merge_request_diff_comment Rate-limited

add_merge_request_diff_comment stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "add_merge_request_diff_comment": {
      "limits": [
        {
          "counter": "add_merge_request_diff_comment_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches GitLab MR MCP, so you can run agents against it safely.

FAQ

Questions about add_merge_request_diff_comment

What does the add_merge_request_diff_comment tool do? +

Add a comment of a merge request at a specific line in a file diff. It is categorised as a Write tool in the GitLab MR MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on add_merge_request_diff_comment? +

Register the GitLab MR MCP server in PolicyLayer and add a rule for add_merge_request_diff_comment: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches GitLab MR MCP. Nothing to install.

What risk level is add_merge_request_diff_comment? +

add_merge_request_diff_comment is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit add_merge_request_diff_comment? +

Yes. Add a rate_limit block to the add_merge_request_diff_comment rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block add_merge_request_diff_comment completely? +

Set action: deny in the PolicyLayer policy for add_merge_request_diff_comment. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides add_merge_request_diff_comment? +

add_merge_request_diff_comment is provided by the GitLab MR MCP server (kevinlin/gitlab-mr-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.