createLambdaWithId
Creates a Lambda. You can optionally specify an Id for the lambda, if not provided one will be generated.
This record as markdown: /tools/io-fusionauth-mcp-api/createlambdawithid.md
What createLambdaWithId does on Fusionauth
AI agents use createLambdaWithId 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.
Why createLambdaWithId is rated Medium
This tool creates new lambda functions in FusionAuth, which is a reversible write operation (lambdas can be deleted/modified later). However, the severity is high because maliciously created lambdas could be used to inject arbitrary code execution into authentication flows, even though the tool itself is categorized as Write rather than Execute.
From the tool's definition Tool description states 'Creates a Lambda' — a write operation that creates new data (lambda functions). The optional Id parameter allows specification but the core action is object creation.
Attacks that exploit this kind of access
The rule that runs createLambdaWithId 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 createLambdaWithId, this is the rule to start with:
createLambdaWithId 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.
The button opens the PolicyLayer dashboard: create your workspace, connect Fusionauth, apply this rule, and every createLambdaWithId call is checked against it from then on.
Questions about createLambdaWithId
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.
Register the Fusionauth MCP server in PolicyLayer and add a rule for createLambdaWithId: 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.
createLambdaWithId is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the createLambdaWithId 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 createLambdaWithId. 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.
createLambdaWithId 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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