We make the invisible visible.
Replay started with a simple belief: if you can't see what your software is doing, you can't fix it. We built the technology to change that — for developers, for AI agents, and for anyone building with code.
Where we started
Debugging has always been the same: guess what went wrong, try a fix, see if it works. Repeat until you get lucky or give up and rewrite.
We thought that was broken. Our founders spent a decade at Mozilla working on the Firefox browser engine — one of the most complex software systems ever built. They saw firsthand how much time gets lost to bugs that nobody can reproduce, errors that nobody can explain, and fixes that nobody is confident about.
So they built Replay: a way to record exactly what your software did and play it back, step by step. Not a video. Not a log file. A deterministic capture of every DOM change, network request, and state update — the full picture, down to the last detail.
In the early days, we gave developers a superpower: the ability to time travel through their recordings. Step forward, step back, inspect state at any point in time. No reproduction required. No guessing. Just the truth.
Where we're going
Today, AI agents write code faster than any human. But when a test fails in CI, they're stuck — guessing at fixes with no way to see what went wrong at runtime. They loop, retry, and burn through tokens on the same mistake.
So we gave the time machine to the agent. Replay now enables your coding agent to time-travel through recordings and fix failing tests without human intervention. It turns out they're way better at it anyway — no fatigue, no missed details, no wrong turns.
The Replay CI Agent watches every PR. When a test fails, it records the full runtime, analyzes the execution, and posts the root cause plus a specific fix as a PR comment. Replay MCP brings the same time-travel capability directly into your IDE, where your coding agent already works.
We're building toward a world where every test failure comes with a root cause, every broken PR gets a fix, and no one — human or AI — has to debug blind.
How we work
The principles behind the product.
Clarity over cleverness
We build tools that show you exactly what happened — no abstractions, no hand-waving. That same principle runs through everything we do: our code, our communication, and our product.
Long-term over fast
We're not optimizing for the next quarter. We're building technology that changes how software gets built and debugged. That takes patience, and we're built for it.
Open over closed
We're a distributed team across time zones and continents. We care about what you ship, not when you're online. And we believe the tools that make software understandable should be accessible to everyone — not just engineers at big companies.
The team
Founded by ex-Mozilla engineers. Distributed globally. Building the future of debugging.
Brian HackettCEO
Stanford Ph.D. with 10 years at Mozilla, where he worked on the systems that power the Firefox browser engine. Brian started Replay to solve the problem he spent a decade fighting: helping developers understand complex systems when things go wrong. When he's not building Replay, he's sailing or traveling in a van.
Mark EriksonSoftware Engineer
The maintainer of Redux and creator of Redux Toolkit — tools used by millions of React developers worldwide. Mark brings deep expertise in developer tooling and an obsessive focus on developer experience. Based in Southwest Ohio.
Dominik SeifertSoftware Engineer
Two decades of software engineering, from MMORPG servers to CUDA optimization. Dominik holds a Ph.D. in systems analysis and brings the kind of low-level systems knowledge that makes Replay's recording engine possible. Based in Taiwan, originally from Germany.
Thomas DalyHead of Product
Thomas is a product builder/maker that lives at the intersection of the customer and the product, while reading the tea leaves of the shifting landscape. Obsessed with the details of making great things, and loves nothing more than to do with good people. He talks about hospitality vs. hostility a lot. He lives in the lower Hudson River valley in NY.
Strider WilsonSoftware Engineer
Frontend Software Engineer focused on building clean, intuitive user experiences that make complex technology feel simple. Strider specializes in React, TypeScript, and modern UI architecture, turning ambitious ideas into polished, scalable products. With experience across startups, product design, and fast-moving engineering teams, he enjoys solving hard problems through thoughtful design and efficient code. Outside of tech, he brings an adventurous mindset shaped by years as a wingsuit BASE jumper, skydiving instructor, photographer, and creator.
- The code behind our code
Integrity, honesty, and decency. Our principles are not aspirations but constraints. They lie behind every action we take, or decision we make. They ensure that we remain true to our course and true to ourselves.
- Embedded values
Our values anchor our aspirations and drive us forward.
We are making software development faster, more accessible, more inclusive, and more exciting. We are dedicated to building a world where everyone is technically literate, a world where we are better equipped to overcome the greatest of challenges.
See what your software is doing.
Install the CI Agent on your repo, or add Replay MCP to your coding agent. Free to get started.