createLambda

Creates a Lambda. You can optionally specify an Id for the lambda, if not provided one will be generated.

SERVERFusionauth SOURCE@fusionauth/mcp-api

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/io-fusionauth-mcp-api/createlambda.md

WHAT IT DOES

What createLambda does on Fusionauth

AI agents use createLambda to create or update resources in Fusionauth, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Fusionauth environment.

RISK

Why createLambda is rated Medium

This tool creates a Lambda function in FusionAuth, which is a piece of code that can be injected into the authentication/authorization pipeline. While it is a reversible write operation, the severity is high because creating a malicious lambda could intercept authentication flows, steal credentials, or manipulate JWT claims across all users in the system.

From the tool's definition Creates a Lambda. You can optionally specify an Id for the lambda, if not provided one will be generated.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs createLambda safely

PolicyLayer is an MCP gateway: it sits between your AI agents and Fusionauth, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For createLambda, this is the rule to start with:

createLambda Rate-limited

createLambda stays usable, but capped: an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "createLambda": {
      "limits": [
        {
          "counter": "createlambda_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Fusionauth, apply this rule, and every createLambda call is checked against it from then on.

FAQ

Questions about createLambda

What does the createLambda tool do? +

Creates a Lambda. You can optionally specify an Id for the lambda, if not provided one will be generated. It is categorised as a Write tool in the Fusionauth MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on createLambda? +

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

What risk level is createLambda? +

createLambda is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit createLambda? +

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

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

createLambda is provided by the Fusionauth MCP server (@fusionauth/mcp-api). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

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