// MCP TOOL REFERENCE

stream_trim

Trim stream to specified length. Args: key: The name of the key maxlen: Maximum length to trim to approximate: Whether maxlen is approximate Returns: Success message or error message

ServerAWS
CategoryDestructive

How to control stream_trim ↓

WHAT IT DOES

What stream_trim does on AWS

AI agents call stream_trim to permanently remove resources in AWS — typically in cleanup and lifecycle workflows. It does its job in a single call, and there is no undo.

THE RISK

Critical Risk

Why stream_trim needs a policy

Trimming a stream irreversibly removes older entries beyond the specified length. This data loss cannot be undone, making it a Destructive operation. High severity because an agent could set maxlen=0 or a very small value, wiping out all or most stream data.

From the tool's definition Trim stream to specified length — removes/discards entries from the stream that exceed the specified maxlen

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

POLICY

How to control stream_trim

PolicyLayer is an MCP gateway — it sits between your AI agents and AWS, and nothing reaches the server without passing your rules. This is the rule we recommend for stream_trim:

policy.json

{
  "version": "1",
  "default": "deny",
  "hide": [
    "stream_trim"
  ]
}

stream_trim disappears from the agent's tool list entirely, and any attempt to call it is denied. The rest of the server keeps working.

Create a free account and register AWS — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

RESTRICT THIS TOOL →

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EXPLORE

Related tools and policies

More AWS tools

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All 300 AWS tools →

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Go deeper

Govern infrastructure agents → Production lockdown, region locks, and approval-to-delete on every infrastructure call agents make.
Critical-risk tools in AWS → Every critical-risk tool this server exposes, in one view.
All critical-risk MCP tools → Every critical-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Blast radius → How much damage one compromised or confused agent can do — and how to bound it.
Tool call approval → Approval gates on individual tool calls: auto-allow, prompt, or deny.
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 stream_trim

What does the stream_trim tool do? +

Trim stream to specified length. Args: key: The name of the key maxlen: Maximum length to trim to approximate: Whether maxlen is approximate Returns: Success message or error message. It is categorised as a Destructive tool in the AWS MCP Server, which means it can permanently delete or destroy data. Block by default and require explicit approval.

How do I enforce a policy on stream_trim? +

Register the AWS MCP server in PolicyLayer and add a rule for stream_trim: 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 AWS. Nothing to install.

What risk level is stream_trim? +

stream_trim is a Destructive tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.

Can I rate-limit stream_trim? +

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

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

stream_trim is provided by the AWS MCP server (@awslabs/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every AWS tool call.

Start from AWS, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

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