start_neb · Fairchem MCP: Risk & Policy

WHAT IT DOES

What start_neb does on Fairchem

AI agents invoke start_neb to trigger actions in Fairchem. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why start_neb needs a policy

NEB is a computationally expensive simulation that runs external calculations and modifies system state (calculates energy barriers, reaction pathways). While not permanently destructive to stored data, it executes arbitrary computational operations whose outcomes depend entirely on user-supplied arguments (atomic structures, force fields via sibling tools like 'attach_emt' or 'attach_lammps').

From the tool's definition Tool is part of a computational simulation server that executes NEB (Nudged Elastic Band) calculations. Context clues: (1) sibling tool 'execute' suggests this server runs code/simulations; (2) 'start_neb' initiates a complex multi-step external operation…

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

start_neb Rate-limited

start_neb stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "start_neb": {
      "limits": [
        {
          "counter": "start_neb_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Fairchem, so you can run agents against it safely.

FAQ

Questions about start_neb

What does the start_neb tool do? +

start_neb. It is categorised as a Execute tool in the Fairchem MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on start_neb? +

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

What risk level is start_neb? +

start_neb is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit start_neb? +

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

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

start_neb is provided by the Fairchem MCP server (jkitchin/fairchem-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.