storage · Nextjs Agent MCP: Risk & Policy

WHAT IT DOES

What storage does on Nextjs Agent

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

WHY IT NEEDS A POLICY

Why storage needs a policy

This tool permits modification of browser-side persistent data. While the changes are reversible (storage can be cleared or reset), an AI agent could inject malicious session tokens, modify authentication state, or inject data that alters application behavior. This is a Write operation rather than Destructive because the data is not permanently deleted—it is modified and could theoretically be reverted.

From the tool's definition Tool description states 'Read or modify browser storage in a tab' — the word 'modify' indicates write capability. Browser storage (localStorage, sessionStorage, cookies) can be altered reversibly.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

storage Rate-limited

storage 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": {
    "storage": {
      "limits": [
        {
          "counter": "storage_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 Nextjs Agent, so you can run agents against it safely.

FAQ

Questions about storage

What does the storage tool do? +

Read or modify browser storage in a tab. It is categorised as a Write tool in the Nextjs Agent MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on storage? +

Register the Nextjs Agent MCP server in PolicyLayer and add a rule for storage: 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 Nextjs Agent. Nothing to install.

What risk level is storage? +

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

Can I rate-limit storage? +

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

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

storage is provided by the Nextjs Agent MCP server (zohaib3249/nextjs-agent-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.