generate_image · Banana Image MCP: Risk & Policy

WHAT IT DOES

What generate_image does on Banana Image MCP

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

WHY IT NEEDS A POLICY

Why generate_image needs a policy

This tool creates new image artifacts and persists them to cloud storage (Qiniu CDN), making it a Write operation that modifies external state. While it uses AI generation as an intermediate step, the primary effect is persistent data creation. Severity is medium because misuse could result in unauthorized image generation and CDN storage consumption, but the operation is reversible (images can be deleted).

From the tool's definition Tool description explicitly states the tool 'upload to Qiniu CDN' and 'return the CDN URL', indicating it creates and stores new data. The sibling tool 'upload_image' confirms this server writes to external storage systems.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

generate_image Rate-limited

generate_image 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": {
    "generate_image": {
      "limits": [
        {
          "counter": "generate_image_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 Banana Image MCP, so you can run agents against it safely.

FAQ

Questions about generate_image

What does the generate_image tool do? +

Generate an image using Google Gemini AI, convert to WebP format, upload to Qiniu CDN, and return the CDN URL. It is categorised as a Write tool in the Banana Image MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on generate_image? +

Register the Banana Image MCP server in PolicyLayer and add a rule for generate_image: 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 Banana Image MCP. Nothing to install.

What risk level is generate_image? +

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

Can I rate-limit generate_image? +

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

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

generate_image is provided by the Banana Image MCP server (xinpengfei520/banana-image-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.