witness_append · Claude Flow MCP: Risk & Policy

WHAT IT DOES

What witness_append does on Claude Flow

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

WHY IT NEEDS A POLICY

Why witness_append needs a policy

Appending to a witness chain is a Write operation: it adds new entries to an existing data structure (likely an audit/event log or cryptographic chain). It does not delete or overwrite existing data, does not execute code, and has no financial implications.

From the tool's definition 'Append to witness chain' — the word 'append' indicates adding data to an existing structure (a witness chain), which is a write/create operation.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

witness_append Rate-limited

witness_append 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": {
    "witness_append": {
      "limits": [
        {
          "counter": "witness_append_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 Claude Flow, so you can run agents against it safely.

FAQ

Questions about witness_append

What does the witness_append tool do? +

Append to witness chain. It is categorised as a Write tool in the Claude Flow MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on witness_append? +

Register the Claude Flow MCP server in PolicyLayer and add a rule for witness_append: 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 Claude Flow. Nothing to install.

What risk level is witness_append? +

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

Can I rate-limit witness_append? +

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

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

witness_append is provided by the Claude Flow MCP server (claude-flow). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.