This record as markdown: /tools/aws/stream-trim.md
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.
Why stream_trim is rated Critical
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
Attacks that exploit this kind of access
The rule that runs stream_trim safely
PolicyLayer is an MCP gateway: it sits between your AI agents and AWS, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For stream_trim, this is the rule to start with:
stream_trim is removed from the agent's tool list entirely, so the agent never calls it. The rest of the server keeps working.
The button opens the PolicyLayer dashboard: create your workspace, connect AWS, apply this rule, and every stream_trim call is checked against it from then on.
Questions about 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. 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.
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.
stream_trim is a Destructive tool with critical risk. Critical-risk tools should be blocked by default and only enabled with explicit human approval.
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.
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.
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.
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