fill_pdf_form · Nexus Core MCP: Risk & Policy

WHAT IT DOES

What fill_pdf_form does on Nexus Core

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

WHY IT NEEDS A POLICY

Why fill_pdf_form needs a policy

The tool modifies a PDF by filling in form fields and persisting the result to disk. This is a Write operation because: (1) it creates or modifies data (filling form fields), (2) the operation is reversible (the output can be regenerated or deleted), and (3) it does not execute arbitrary code, delete data irreversibly, or move financial resources.

From the tool's definition Tool description states it "Fill[s] AcroForm fields in input_path PDF and save[s] to output_path", which involves modifying PDF content and writing to a specified output file. This is a reversible creation/modification operation.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

fill_pdf_form Rate-limited

fill_pdf_form 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": {
    "fill_pdf_form": {
      "limits": [
        {
          "counter": "fill_pdf_form_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 Nexus Core, so you can run agents against it safely.

FAQ

Questions about fill_pdf_form

What does the fill_pdf_form tool do? +

Fill AcroForm fields in input_path PDF and save to output_path. It is categorised as a Write tool in the Nexus Core MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on fill_pdf_form? +

Register the Nexus Core MCP server in PolicyLayer and add a rule for fill_pdf_form: 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 Nexus Core. Nothing to install.

What risk level is fill_pdf_form? +

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

Can I rate-limit fill_pdf_form? +

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

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

fill_pdf_form is provided by the Nexus Core MCP server (noumenon-ai/nexus-core). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.