cache_replace · Awslabs Valkey MCP: Risk & Policy

WHAT IT DOES

What cache_replace does on Awslabs Valkey

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

WHY IT NEEDS A POLICY

Why cache_replace needs a policy

This tool modifies existing data in the cache by replacing a value, which is a reversible write operation. It does not delete data (so not Destructive), does not execute arbitrary code (so not Execute), and does not involve financial transactions (so not Financial).

From the tool's definition Tool name 'cache_replace' and description 'Replace a value in the cache only if the key exists' indicates modification of cached data.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

cache_replace Rate-limited

cache_replace 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": {
    "cache_replace": {
      "limits": [
        {
          "counter": "cache_replace_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 Awslabs Valkey, so you can run agents against it safely.

FAQ

Questions about cache_replace

What does the cache_replace tool do? +

Replace a value in the cache only if the key exists. It is categorised as a Write tool in the Awslabs Valkey MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on cache_replace? +

Register the Awslabs Valkey MCP server in PolicyLayer and add a rule for cache_replace: 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 Awslabs Valkey. Nothing to install.

What risk level is cache_replace? +

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

Can I rate-limit cache_replace? +

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

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

cache_replace is provided by the Awslabs Valkey MCP server (awslabs.valkey-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.