hcs_write_record · Hedera Toolbox MCP: Risk & Policy

WHAT IT DOES

What hcs_write_record does on Hedera Toolbox

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

WHY IT NEEDS A POLICY

Why hcs_write_record needs a policy

This tool creates/appends new data (compliance records) to the blockchain, which is reversible in the sense that subsequent records can be written, but the individual record itself cannot be deleted or modified once committed. It falls under Write rather than Destructive because the intent is record creation, not erasure.

From the tool's definition 'Write a tamper-evident compliance record to the Hedera blockchain' — the verb 'write' and explicit record creation to a blockchain ledger indicate data modification.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

hcs_write_record Rate-limited

hcs_write_record 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": {
    "hcs_write_record": {
      "limits": [
        {
          "counter": "hcs_write_record_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 Hedera Toolbox, so you can run agents against it safely.

FAQ

Questions about hcs_write_record

What does the hcs_write_record tool do? +

Write a tamper-evident compliance record to the Hedera blockchain. Returns a. It is categorised as a Write tool in the Hedera Toolbox MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on hcs_write_record? +

Register the Hedera Toolbox MCP server in PolicyLayer and add a rule for hcs_write_record: 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 Hedera Toolbox. Nothing to install.

What risk level is hcs_write_record? +

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

Can I rate-limit hcs_write_record? +

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

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

hcs_write_record is provided by the Hedera Toolbox MCP server (mountainmystic/hederatoolbox). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.