list_schemas | PolicyLayer

WHAT IT DOES

What list_schemas does on Amazon Bedrock Knowledge Base Retrieval MCP Server

AI agents call list_schemas to retrieve information from Amazon Bedrock Knowledge Base Retrieval MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.

THE RISK

Low Risk

Why list_schemas needs a policy

The tool appears to retrieve or enumerate schema metadata from the knowledge base, consistent with Read category operations (list, get, fetch). The empty description prevents higher confidence, but the name strongly suggests a non-destructive retrieval. Severity is low because schema enumeration typically has minimal blast radius unless schemas contain highly sensitive metadata.

From the tool's definition Tool name 'list_schemas' indicates a query/listing operation. Description is empty, limiting certainty, but the verb 'list' is a canonical Read operation that retrieves schema information without modification.

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

POLICY

How to control list_schemas

PolicyLayer is an MCP gateway — it sits between your AI agents and Amazon Bedrock Knowledge Base Retrieval MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for list_schemas:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "list_schemas": {}
  }
}

list_schemas is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

Create a free account and register Amazon Bedrock Knowledge Base Retrieval 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.

CAP THIS TOOL →

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EXPLORE

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Go deeper

Roll out MCP under one policy → Per-person scoped tokens, one central policy, and full audit across every server your team connects.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →
PolicyLayer vs alternatives → How deterministic, per-call MCP policy compares with gateways, identity layers, and authorisation platforms.

FAQ

Questions about list_schemas

What does the list_schemas tool do? +

list_schemas. It is categorised as a Read tool in the Amazon Bedrock Knowledge Base Retrieval MCP Server MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on list_schemas? +

Register the Amazon Bedrock Knowledge Base Retrieval MCP Server MCP server in PolicyLayer and add a rule for list_schemas: 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 Amazon Bedrock Knowledge Base Retrieval MCP Server. Nothing to install.

What risk level is list_schemas? +

list_schemas is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit list_schemas? +

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

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

list_schemas is provided by the Amazon Bedrock Knowledge Base Retrieval MCP Server MCP server (awslabs.bedrock-kb-retrieval-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 Amazon Bedrock Knowledge Base Retrieval MCP Server tool call.

Start from Amazon Bedrock Knowledge Base Retrieval MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

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805 Amazon Bedrock Knowledge Base Retrieval MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.