modify_trace

THE RISK

Medium Risk

Why modify_trace needs a policy

This tool modifies PCB trace properties (width, layer, net assignments) which are design parameters that can be undone or reverted in KiCAD. It does not delete traces (which would be Destructive), execute code (Execute), or move money (Financial).

From the tool's definition Tool name 'modify_trace' and description state it 'Modify an existing trace (change width, layer, or net)' — this reversibly alters PCB design data without deleting or executing arbitrary operations.

Documented attack patterns abuse exactly the kind of access modify_trace gives an agent:

POLICY

How to control modify_trace

PolicyLayer is an MCP gateway — it sits between your AI agents and KiCAD-MCP-Server, and nothing reaches the server without passing your rules. This is the rule we recommend for modify_trace:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "modify_trace": {
      "limits": [
        {
          "counter": "modify_trace_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

modify_trace 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.

Create a free account and register KiCAD-MCP-Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More KiCAD-MCP-Server tools

Destructive delete_component Remove a component from the PCB by its reference designator. Destructive delete_schematic_component Remove a placed symbol from a KiCAD schematic (.kicad_sch). This removes the symbol insta Destructive delete_schematic_net_label Remove a net label from the schematic. Destructive delete_schematic_wire Remove a wire from the schematic by start and end coordinates. Destructive delete_symbol Remove a symbol from a .kicad_sym library file. Destructive delete_trace Delete traces from the PCB. Can delete by UUID, position, or bulk-delete all traces on a n Destructive remove_schematic_component_property Remove a single custom property from a placed schematic symbol. Built-in fields (Referenc Execute autoroute Run Freerouting autorouter on the current PCB. Exports to Specctra DSN, runs Freerouting C

All 157 KiCAD-MCP-Server tools →

Write tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about modify_trace

What does the modify_trace tool do? +

Modify an existing trace (change width, layer, or net). It is categorised as a Write tool in the KiCAD-MCP-Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on modify_trace? +

Register the KiCAD-MCP-Server MCP server in PolicyLayer and add a rule for modify_trace: 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 KiCAD-MCP-Server. Nothing to install.

What risk level is modify_trace? +

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

Can I rate-limit modify_trace? +

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

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

modify_trace is provided by the KiCAD-MCP-Server MCP server (mixelpixx/kicad-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every KiCAD-MCP-Server tool call.

Start from KiCAD-MCP-Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →