AI agents invoke sam_local_invoke to trigger actions in AWS Step Functions Tool MCP Server. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.
SAM local invocation executes application code—potentially arbitrary Lambda functions—whose effects depend on function arguments and environment configuration. This is categorized as Execute rather than Write or Read because it triggers external operations (function invocation) beyond simple data retrieval or modification.
From the tool's definition Tool name 'sam_local_invoke' indicates invocation of AWS SAM (Serverless Application Model) functions locally.
Documented attack patterns abuse exactly the kind of access sam_local_invoke gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and AWS Step Functions Tool MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for sam_local_invoke:
{
"version": "1",
"default": "deny",
"tools": {
"sam_local_invoke": {
"limits": [
{
"counter": "sam_local_invoke_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}sam_local_invoke stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
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sam_local_invoke. It is categorised as a Execute tool in the AWS Step Functions Tool MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the AWS Step Functions Tool MCP Server MCP server in PolicyLayer and add a rule for sam_local_invoke: 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 Step Functions Tool MCP Server. Nothing to install.
sam_local_invoke is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the sam_local_invoke 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 sam_local_invoke. 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.
sam_local_invoke is provided by the AWS Step Functions Tool MCP Server MCP server (awslabs.stepfunctions-tool-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from AWS Step Functions Tool 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 AWS Step Functions Tool MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.