write_create_comment · Langfuse MCP Server MCP

WHAT IT DOES

What write_create_comment does on Langfuse MCP Server

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

WHY IT NEEDS A POLICY

Why write_create_comment needs a policy

This tool creates new comments within Langfuse, modifying project state but not destructively. Comments can be deleted or edited, making this a reversible Write operation rather than Destructive. The blast radius is medium—an AI agent could add many comments or spam traces, but this doesn't cause data loss or financial impact. Confidence is high due to explicit 'write operation' language in the description.

From the tool's definition Tool description states 'Create a comment on a trace, observation, session, or prompt. This write operation will modify your Langfuse project.' The explicit mention of 'write operation' and 'will modify your Langfuse project' confirms this creates new data…

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

write_create_comment Rate-limited

write_create_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": {
    "write_create_comment": {
      "limits": [
        {
          "counter": "write_create_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 Langfuse MCP Server, so you can run agents against it safely.

FAQ

Questions about write_create_comment

What does the write_create_comment tool do? +

Create a comment on a trace, observation, session, or prompt. This write operation will modify your Langfuse project. It is categorised as a Write tool in the Langfuse MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on write_create_comment? +

Register the Langfuse MCP Server MCP server in PolicyLayer and add a rule for write_create_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 Langfuse MCP Server. Nothing to install.

What risk level is write_create_comment? +

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

Can I rate-limit write_create_comment? +

Yes. Add a rate_limit block to the write_create_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 write_create_comment completely? +

Set action: deny in the PolicyLayer policy for write_create_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 write_create_comment? +

write_create_comment is provided by the Langfuse MCP Server MCP server (therealsachin/langfuse-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.