Workers IO

Engineering teams building systems that require very high uptime, such as fintech, infrastructure, and e-commerce platforms, cannot fully test how their systems behave under rare combinations of network faults, timing issues, crashes, and retries. Bugs like double charges, lost writes, or missing receipts often only surface in production under specific interleavings of failures that are hard to reproduce or reason about in advance. Today these teams likely rely on manual testing, incident postmortems, or ad hoc fault injection that does not systematically search the space of possible failure conditions. When something breaks, reproducing the exact sequence of events that caused it can be difficult, slowing down root cause analysis and fixes.

Workers IO runs a team's system inside deterministic virtual machines and simulates millions of realistic production scenarios, injecting faults like dropped network calls, killed databases, and service blackholes to see whether the system's core invariants still hold. Users define explicit promises the system must never break, such as money_conserved or charged_once, and the platform reports pass or fail across many seeds, pinpointing exact failure conditions like a specific seed where a receipt was never written after a successful retry. Every failed run is fully reproducible, including the injected faults, execution trace, and dependency return values, so engineers can shrink the failure to its root cause in the actual source code and verify a fix under the same conditions. The platform also integrates with coding agents through a GitHub skills repo, so changes proposed by agents are verified against the same simulated scenarios before release, with failures returned as replayable cases.