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Your E2E tests fail.
Replay tells you why —
and how to fix it.

Replay CI Agent automatically records every test run, analyzes failures using time-travel debugging data, and posts a root cause, failure trace, and suggested fix as a comment on your PR.

Try Replay for free →

Start free. No credit card required. $299/mo for Growth.

Trusted by top engineering teams

Your CI fails.
Your team debugs. Repeat.

A test fails in CI. The test assertion tells you what failed—not what broke. Someone opens DevTools, reproduces it locally if they're lucky, and eventually figures out the root cause. That's an hour per failure. Multiply by your team.

Your coding agents make this worse. They can write code faster than ever, but when something breaks at runtime they're debugging blind — guessing at fixes, looping on the same failure, burning tokens without making progress. The bottleneck isn't writing code. It's what happens when it breaks.

So teams do the rational thing: they avoid writing more automated tests, because the maintenance overhead isn't worth it. Coverage stagnates. Confidence erodes.

That's why we built Replay

Give your agent the power of time-travel

Replay captures a deterministic recording — every DOM change, network request, JS execution frame, and state update. Using Replay MCP, your coding agent can analyze the recording, trace the exact causal chain from failure to root cause, and deliver the root cause and a suggested fix. No guessing. No manual debugging. No human required.

You might be thinking “how is that different than the monitoring tools I'm already using?” We made this video for you.

Every CI failure, automatically analyzed

Replay does the investigation. Your team gets the root cause and a suggested fix — without spending hours debugging.

Test fails — Replay records

Every Playwright run in CI is recorded automatically. When a test fails, the full runtime is captured — DOM mutations, network calls, JS execution frames. No changes to your test code.

Replay analyzes the recording

Replay's agent steps through the execution using time-travel debugging data, identifies the exact sequence of events that caused the failure, and determines the root cause with a confidence score.

Root cause + suggested fix posted to your PR

Replay comments on your PR with its findings — root cause, evidence trail, and a suggested fix with specific file and line references. Your team reads the comment and applies the fix.

Replay CI Agent posting root cause analysis and suggested fix as a GitHub PR comment

Analysis that used to require a staff engineer

Three classes of runtime bugs that require seeing the actual execution — not a trace. Now deliverable by your coding agent.

Render-to-cause chains

Why did this component re-render 14 times? Trace it backward through the dependency graph to the exact state mutation. Not a guess — the actual render line at the moment it happened.

Component re-rendered 14 times on a single click. Root cause: useState returned a new object reference on every call. useSelector was never memoized.

Selector reference tracking

Which selector read stale data? When did it change? Replay tracks every reference so your agent answers these questions without adding a single log line to your codebase.

Selector: UserPermissions returned the wrong value at t+340ms. The auth slice updated at t+320ms but the selector cache wasn't invalidated.

JS execution, frame by frame

Step through any JavaScript frame in order. Add console logs retroactively. Set breakpoints that didn't exist when the bug happened. This is impossible with logs — it requires the recording.

The race condition is in PaymentFlow.tsx line 32. The onSubmit handler fires before the async validation resolves. Here's the fix:

From bug to fix — without touching DevTools

See how Replay MCP lets your agent dive in and explain the problem.

Button doesn't work

Creating a new task does nothing

Chat transcript with Replay MCP

The form to add a new task isn't doing anything

I'll investigate why the form to add a new task isn't working. Let me start by exploring the recording to understand what's happening.

Let me look at the CreateTaskModal component more closely to understand its implementation, especially the form submission logic.

I can see the form submission logic. Line 53-54 shows handleSubmit was called once, but let me check where the onSave callback leads to. Let me look at TasksListPage to see how the modal's onSave is handled.

I found the issue! Looking at handleCreateTask (lines 73-93):

  1. Line 83 shows the function was called once (hit count: 1)
  2. Lines 84-90 build the payload object
  3. Line 92 closes the modal with setCreateModalOpen(false) (hit count: 1)
  4. But there's no fetch call to actually save the task!

The function closes the modal at the end, but it never makes a network request to persist the new task. The payload is built but never sent to the server.

Root Cause

The handleCreateTask function in TasksListPage.tsx is missing the API call to create the task. It:

  1. Builds the payload object ✓
  2. Closes the modal ✓
  3. Does NOT call fetch to POST the task to the backend

Compare this to line 65-70 where fetch is used to load deals - a similar pattern should exist after building the payload on line 92, but it's missing. The function just closes the modal without actually saving anything.

What developers are saying

Teams at Vercel, Glide, Tablecheck, Pantheon, and more use Replay every day.

Before Replay, we spent somewhere between 1–2 hours per day per dev in this reproducibility purgatory.

Mark Probst

VP Engineering, Glide

The tools that we were using before were barely better than useless. You'd say thanks for the console log screenshots and spend 2–3 days trying to recreate the issues.

Shane Duff

Front End Lead, Pantheon

Next.js App Router is now stable in 13.4. It wouldn't have been possible without Replay, we investigated so many super complicated bugs.

Tim Neutkens

Co-author of Next.js, Vercel

Replay.io is galaxy brain tooling. Real gamechanger.

Dan Abramov

React Maintainer

After seeing what Replay can do, I'm going to set up a lot more Playwright tests on my PRs. Was afraid to before, due to the extra work of debugging failed tests.

Ben Buckman

Co-founder, setmefree.com

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

Time Travelogue: How Replay MCP Helped Find a React Bug Faster than Dan Abramov Did

Featured proof point

Replay solved a bug that stumped Dan Abramov

Dan had been manually debugging a React 19 race condition. Replay's agent traced it to root cause in 7 minutes — using the same time-travel recording data that powers our CI Agent analysis. The analysis identified the exact fix without any human intervention.

Read the full story →

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

Dan Abramov

React Maintainer

Debugging a specific bug?

Replay also works for individual developers hunting down hard-to-reproduce bugs. Connect Replay MCP to your coding agent and it can step through any recorded execution — same time-travel data, directly in your IDE.

Learn how it works for individual debugging →

Time travelogues

Deep-dive time-travel sessions

A running series of real debugging investigations — each one pitting Replay MCP against a bug that stumped a human expert.

7 min

Replay MCP solved a React bug faster than Dan Abramov did

Replay MCP agent looked at a React 18 issue, and found root cause in a little over 7 minutes. Dan had been manually debugging the same bug.

Read the story →

Mark Erikson

4–9 min

The architectural fix Nadia spent days finding — solved automatically

Given a Replay recording and codebase, an AI agent recommended the exact server-side prefetching fix Nadia had eventually discovered through days of intense investigation.

Read the story →

Mark Erikson

With Replay CI Agent vs. without

Without Replay

  • Test fails → read error message, guess at cause
  • Root cause requires manual reproduction, console logs, trial and error
  • 30 min to 2+ hours per failure
  • Flaky tests get marked as flaky, ignored, accumulate
  • PRs blocked, CI re-runs burn time and money
  • Requires deep codebase knowledge to investigate

With Replay CI Agent

  • Test fails → agent traces exact failure sequence
  • Root cause identified automatically with confidence score
  • Fix suggestion posted in minutes
  • Each failure investigated individually with runtime evidence
  • Developer reads comment, applies fix, merges
  • Zero investigation effort — agent does the work

Fits your existing CI pipeline

Swap in Replay in your Playwright or Cypress config and install the GitHub bot. No changes to your test code.

Test frameworks & CI

PlaywrightCypressGitHub ActionsCircleCIJenkins

Coding agents

Claude CodeCodexCursorCopilotWindsurf

Common questions

Replay works by swapping in a Replay-instrumented browser in your CI config. When a test runs, Replay captures every DOM mutation, network request, and JS execution deterministically — so the recording is a perfect, replayable trace of exactly what happened.

Stop debugging test failures manually.

Free plan available. No credit card required. $299/mo for Growth.