An all seeing debugger for your web app

We're building Nut, a chat API for explaining problems in your app. Nut records your app to capture and later analyze the billions of things that happened while it ran, then tells you the root cause. Take the actual work out of figuring out most bugs.


Nut example

Introducing Nut.new

Crack the toughest nuts (bugs)

Nut works especially well with AI code writers. AIs are lousy at debugging problems in code they've written. The basic issue is a lack of context: people use devtools to understand their app, but AIs struggle here. Nut gives AIs the clear explanations they need to fix bugs reliably.

For now we're focusing on Nut.new, a no-code tool in the mold of Boltv0, and Lovable. You can build complete apps from scratch by prompting the AI, and call the Nut API to get past the points where other tools get stuck. Nut.new is free to use lightly, and in unlimited amounts through our early adopter program or with your own Anthropic API key.

Nut uses our Chromium-based deterministic browser recorder. The browser captures just enough data while your app is running that it can be replayed later and behave exactly the same. This behavior is queried like a database and processed with advanced techniques such as dataflow and control dependency analysis to get to the underlying cause of any problem in the recording.

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Become an early adopter

Nut is early in development. We're offering unlimited free access to Nut.new for early adopters who can give us feedback we'll use to improve Nut. Reach us at hi@replay.io or fill out our contact form to join our early adopter program.

Say goodbye to “works on my machine”

Replay is the first deterministic browser. Once a bug or flaky test is captured, anyone can inspect it with Browser DevTools without having to replicate it locally.

Debug with instant console logs.

Add console logs in your code with a single click with messages that “automagically” appear in the Console. You’ll love how fast the feedback loop is.

Fix flaky Cypress + Playwright tests.

Replay’s built in test timeline helps you inspect test step details and jump from test step actions into your application’s React event handlers.

Fix flaky Cypress + Playwright tests. screenshot

Inspect React components

Bugs can appear at any point in time. Replay’s React panel helps you find the component with first visible issues, inspect its props, and work backwards to the root cause.

Inspect React components screenshot

View network requests

The majority of E2E test failures are caused by backend issues. Replay’s Network monitor helps you find the bad request and inspect the application state at the time.

View network requests screenshot

Battle tested.

Replay helps some of the largest companies record their E2E tests at scale and verify the correctness of mission critical software.

Case Studies

Hear from Replay teams directly

Testimonials

See what time travelers are saying

“Next.js App Router is now stable in 13.4. Wouldn’t have been possible without Replay, we investigated so many (over 20) super complicated bugs that using traditional debugging would have cost us days to investigate.”

Tim Neutkins

@Co-author of Next.js

“I think Replay has a very good chance of creating a new category around collaborative debugging”

Guillermo Rauch

@Founder of Vercel

“When I see a hard-to-reproduce issue in GitHub, I ask for a replay.”

JJ Kasper

@Co-author of Next.js

“If I don't immediately know the answer to a bug, I immediately reach for Replay.io. It's like HMR for repros.”

Sebastian Markbåge

@React Maintainer

“Replay.io is galaxy brain tooling. Real gamechanger.”

Dan Abramov

@React Maintainer