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fault is an Open-Source Rust-powered CLI and AI-MCP server that lets engineers and AI agents team up to ship production-ready code.

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Keep Building Incredible Features

The developer tool that brings operations to your code.

Build Like You Have a Full Team

Get AI-powered review hints on reliability, performance and best practices.

Ground Your Deliveries

Automate SLO-validated scenarios with zero config - preview your feature under fault in seconds.

Replay Incidents with Ease

Swiftly understand how your application reacts by exploring production flakiness locally.

Safely Accelerate Your Innovation

Reliability Engineering for Developers

Explore availability threats right from the start through our builtin fault injection engine. Automate continuous validation and make sure you respect your SLOs.

fault run / fault run llm
fault scenario run

AI-Agent Operational Engineering

Bring a touch of operations into your favourite AI-editor with fault builtin MCP server. Ensure you deliver production-aware code and reduce your AI-Agent delivery time.

fault agent tool
fault agent review

Modern Features for Hybrid Engineering Teams

AI is an evolution in the engineering industry journey. Not a rupture from its past.

  • Fully Open Source

    fault is open-sourced under a permissive license and part of Rebound family. Feel free to contribute to it

  • Made for Engineers

    fault is designed to work equally well with engineers and AI-agents in a team effort.

  • Choose Your LLM

    fault supports OpenAI, Gemini, OpenRouter and ollama. Pick up the LLM that best matches your working style.

  • MCP Server

    Plug fault into any AI-Code editor and help them produce sound production output with fault various tools.

  • Battery Included & Extensible

    Common network faults. Domain-specific faults such as LLM and database included.

  • Complex Scenarios

    Easily schedule complex scenarios by configuring timelines of fault injection.

  • Support Any TCP Protocol

    While fault is well-suited for HTTP, it can be just as easily applied to any TCP-based protocol. Explore how your application reacts.

  • Observability Ready

    fault can be configured to send Open Telemetry traces to your favorite provider. Observe the effect of fault injection in your system.

  • eBPF Support

    Intercept traffic without changing anything in your application with fault's eBPF support. Turn fault injection into a stealth game.

Ready?

Download fault and build production-grade applications now.

Frequently Asked Questions

Everything you need to know about bringing fault into your organization.

What is fault?

fault is a developer product aiming at supporting engineers keep their high-standards.

How is fault delivered?

fault is a Rust-powered command line. It runs natively on Linux, macOSX and Windows.

Is fault open-source?

The fault CLI is free and open-source, using an Apache license, and will remain so. You will pay for any LLM model through your own subscription.

Do you upload my data anywhere?

The fault CLI doesn't send your data or code anywhere. If you use a Cloud-based LLM such as OpenAI, Gemini or Open Router, your code will be sent there partially indeed. If you want to remain fully private, we suggest you use ollama that fault also supports.

What programming language do you support?

Currently fault supports Python, Javascript, TypeScript, go and rust. More languages will likely be added.

Can I use fault without its AI features?

Absolutely. While fault provides AI-specific features, its core capabilities are not tied to AI at all. You can thus use fault to explore your reliability using the CLI directly. fault is made for all kinds of engineers!

Can I contribute to fault?

Yes! fault is open-source and love any kind of contributions. From typos to issue fixes or feature requests. Please join us.

How can we get in touch?

First, please don't hesitate. We love hearing from everyone. Just send-us an email to sylvain@fault-project.com and we'll get back to you in no times.

Explore more

fault is part of the Rebound toolset of open-source projects geared towards more reliabile operations. Two other projects complete the toolbox: Chaos Toolkit - a Chaos Engineering tool - as well as Reliably - a reliability platform. Feel free to explore each of them for a comprehensive approach of your journey.