diary_write · Exocortex MCP: Risk & Policy

WHAT IT DOES

What diary_write does on Exocortex

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

WHY IT NEEDS A POLICY

Why diary_write needs a policy

This tool creates or appends diary entries to persistent storage without destructive intent. It is reversible (entries can be edited or deleted by other tools). While it stores data, it has no impact on code execution, financial systems, or irreversible data loss.

From the tool's definition Tool description explicitly states 'Record a diary entry', which is a create/write operation. The context of a 'personal unified memory system' confirms this writes data (diary entries) that can be modified or overwritten.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

diary_write Rate-limited

diary_write 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": {
    "diary_write": {
      "limits": [
        {
          "counter": "diary_write_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 Exocortex, so you can run agents against it safely.

FAQ

Questions about diary_write

What does the diary_write tool do? +

Record a diary entry for an agent. Call after each session to log what happened,. It is categorised as a Write tool in the Exocortex MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on diary_write? +

Register the Exocortex MCP server in PolicyLayer and add a rule for diary_write: 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 Exocortex. Nothing to install.

What risk level is diary_write? +

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

Can I rate-limit diary_write? +

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

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

diary_write is provided by the Exocortex MCP server (shawnhack/exocortex). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.