set_custom_field · Huly MCP: Risk & Policy

WHAT IT DOES

What set_custom_field does on Huly

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

WHY IT NEEDS A POLICY

Why set_custom_field needs a policy

An AI agent can call set_custom_field faster than any human can review — one bad instruction and it creates or modifies resources in Huly by the hundred, each call as confident as the last.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_custom_field Rate-limited

set_custom_field 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_custom_field": {
      "limits": [
        {
          "counter": "set_custom_field_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 Huly, so you can run agents against it safely.

FAQ

Questions about set_custom_field

What does the set_custom_field tool do? +

Set a custom field value on a document. Requires the document ID, class, field ID (from list_custom_fields), and value. Values are auto-parsed: numbers from numeric strings, booleans from. It is categorised as a Write tool in the Huly 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_custom_field? +

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

What risk level is set_custom_field? +

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

Can I rate-limit set_custom_field? +

Yes. Add a rate_limit block to the set_custom_field 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_custom_field completely? +

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

set_custom_field is provided by the Huly MCP server (@firfi/huly-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.