# Workers IO

> Deterministic simulation environments that verify mission-critical software under millions of production scenarios with replayable failures.

Workers IO provides deterministic simulation testing for mission-critical software. It runs a system inside deterministic virtual machines and searches through interleavings, faults, and timings to find the conditions that break defined guarantees. Every failure is replayable, and the platform is also aimed at giving coding agents a verification feedback loop.

## What It Is

Workers IO is a simulation-based verification platform. Teams define promises their system must keep, such as no lost writes, no double fills, or no split-brain, and the platform runs the system across many seeded scenarios covering timing, network, dependency, retry, crash, and service behavior. Results are reported per invariant, with pass/fail verdicts judged over all attempts, for example a check that fails on 2 of 128 seeds along with the first failing seed.

## Deterministic Replay

The vendor states every failed run is reproducible: the injected faults, the full execution trace, and the return values of each dependency are preserved. Engineers can reproduce a failure, shrink it to the root cause, and verify the fix under the same conditions.

## The Agent Loop

The homepage shows a workflow with coding agents such as Claude Code using a `wio` CLI to run a captured checkout journey across 128 seeds under a fault model, investigate a failing seed, and replay it. Handoff artifacts include a run id, failing seed, the failed check, a debug bundle, and a timeline. Agent skills are published in the workersio/skills GitHub repository.

## Security and Deployment

The vendor lists SOC 2 Type II aligned controls, SSO, encryption, monitoring, VPC support, bring-your-own-cloud simulation runs inside a customer's own cloud and network, and zero data retention by default.

## Features
- Deterministic simulation testing
- Seeded fault injection (network, dependency, crash, timing)
- Invariant checks with per-seed verdicts
- Exact failure replay with execution traces
- Failure shrinking to root cause
- Agent feedback loop via CLI and skills
- Bring your own cloud
- SSO, encryption, and VPC support
- Zero data retention by default

## Integrations
Claude Code, GitHub

## Platforms
CLI, WEB

## Pricing
Subscription-based

## Links
- Website: https://workers.io
- Repository: https://github.com/workersio/skills
- EveryDev.ai: https://www.everydev.ai/tools/workers-io