A web-based service may be enabled for simulating test conditions for sub-operations performed by back-end components. The service may operate in production while being tested. A cookie indicating a sub-operation and an intended test condition for the sub-operation may be included in a request to perform an operation. The cookie may be forwarded from a front-end computing node to a computing node that issues a request to perform the indicated sub-operation. The request to perform the sub-operation may be intercepted. The indicated test condition for the sub-operation may be simulated.