set_journal · jrnl MCP Server MCP: Risk & Policy

WHAT IT DOES

What set_journal does on jrnl MCP Server

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

WHY IT NEEDS A POLICY

Why set_journal needs a policy

This tool modifies internal state (the active journal setting) that persists across subsequent operations. While not creating or deleting data in the traditional sense, it is a reversible write operation that changes system configuration. It is not destructive (the change can be undone), not financial, and not a pure read.

From the tool's definition The tool 'set_journal' performs a state-changing operation that sets or modifies the active journal context for subsequent operations. This is a configuration write that affects how the system behaves going forward.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_journal Rate-limited

set_journal 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": {
    "set_journal": {
      "limits": [
        {
          "counter": "set_journal_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 jrnl MCP Server, so you can run agents against it safely.

FAQ

Questions about set_journal

What does the set_journal tool do? +

Set the active journal for subsequent operations. It is categorised as a Write tool in the jrnl 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 set_journal? +

Register the jrnl MCP Server MCP server in PolicyLayer and add a rule for set_journal: 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 jrnl MCP Server. Nothing to install.

What risk level is set_journal? +

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

Can I rate-limit set_journal? +

Yes. Add a rate_limit block to the set_journal 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 set_journal completely? +

Set action: deny in the PolicyLayer policy for set_journal. 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 set_journal? +

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