list_columns | PolicyLayer

WHAT IT DOES

What list_columns does on Amazon Bedrock Knowledge Base Retrieval MCP Server

AI agents call list_columns 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_columns needs a policy

The naming convention 'list_*' is a strong indicator of a retrieval operation with no side effects. Given the server's purpose (Knowledge Base Retrieval), this tool most likely enumerates columns from a table or data structure, a fundamental read operation. Without evidence of mutation, execution, deletion, or financial impact, this falls squarely in the Read category with low severity.

From the tool's definition Tool name is 'list_columns' which follows standard read-only query patterns (list, get, fetch operations). The tool is part of an AWS Bedrock Knowledge Base Retrieval MCP server, suggesting it retrieves schema or metadata information without modification.

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

POLICY

How to control list_columns

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_columns:

policy.json

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

list_columns 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.

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EXPLORE

Related tools and policies

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All 805 Amazon Bedrock Knowledge Base Retrieval MCP Server tools →

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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_columns

What does the list_columns tool do? +

list_columns. 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_columns? +

Register the Amazon Bedrock Knowledge Base Retrieval MCP Server MCP server in PolicyLayer and add a rule for list_columns: 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_columns? +

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

Can I rate-limit list_columns? +

Yes. Add a rate_limit block to the list_columns 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_columns completely? +

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

list_columns 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.