index.build · TOOL4LM MCP: Risk & Policy

WHAT IT DOES

What index.build does on TOOL4LM

AI agents invoke index.build to trigger actions in TOOL4LM. 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 index.build needs a policy

Building a search index is not a simple read; it processes documents and writes index data structures to storage. It triggers an external computation/build operation whose effects depend on the contents of the sandbox directory.

From the tool's definition "Build MiniSearch index for documents in sandbox directory" — actively builds/constructs an index, triggering a potentially resource-intensive operation that modifies indexed state

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

index.build Rate-limited

index.build 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": {
    "index.build": {
      "limits": [
        {
          "counter": "index.build_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 TOOL4LM, so you can run agents against it safely.

FAQ

Questions about index.build

What does the index.build tool do? +

Build MiniSearch index for documents in sandbox directory. It is categorised as a Execute tool in the TOOL4LM MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on index.build? +

Register the TOOL4LM MCP server in PolicyLayer and add a rule for index.build: 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 TOOL4LM. Nothing to install.

What risk level is index.build? +

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

Can I rate-limit index.build? +

Yes. Add a rate_limit block to the index.build 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 index.build completely? +

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

index.build is provided by the TOOL4LM MCP server (khanhs-234/tool4lm). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.