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
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
The test assertion tells you what failed.
Not why.
Your Playwright test fails. The error says expect(page.getByTestId('submit-btn')).toBeVisible() — timeout after 30 seconds. Why isn't the button there? Could be a dozen reasons.
Your team opens the test, reads the selectors, tries to reproduce locally, adds console.logs, re-runs, waits. Maybe they find it in 20 minutes. Maybe it takes two hours. Maybe they mark it as flaky and move on.
Your coding agent tries to help — but without runtime data, it's guessing from the error message just like you are. It suggests a fix, the test still fails, it tries again, burns tokens, goes in circles.
Meanwhile, PRs sit blocked. CI re-runs burn time and money. The team stops trusting the test suite — failures get ignored, flaky tests accumulate, bad code slips through.
Test fails → Agent investigates → Fix posted
Replay does the investigation. Your team gets the root cause and a suggested fix — without spending hours debugging.
Record
Every E2E test run is automatically recorded — every function call, every DOM mutation, every network request, every state change captured deterministically. No code changes to your tests — just swap in Replay in your Playwright or Cypress config.
Analyze
When a test fails, Replay's agent opens the recording and investigates using time-travel debugging data: every function call, every DOM mutation, every network request, every state change. It traces the exact sequence of events that caused the failure.
Report
The agent posts a detailed analysis as a GitHub comment on your PR: root cause with confidence level, step-by-step failure sequence, suggested fix with specific file and code changes, and an evidence trail citing actual runtime data.
Analysis that used to require a staff engineer
Replay captures deterministic recordings — not screenshots, not logs, but the actual program execution. The agent can inspect:
| Render chains | Which component re-rendered, what triggered it, what changed |
| State flow | Redux actions, React state updates, context changes across the component tree |
| Network timing | Every request and response, with exact payload and timing data |
| JS execution | Every function call on every frame, with arguments and return values |
| DOM mutations | What changed in the DOM, when, and what code caused it |
This isn't guessing from error messages. It's reading the actual execution.
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 setting up a lot more Playwright tests on my PRs. I was afraid to before, due to the extra work of debugging failed tests.”
Ben Ruckman
Co-founder, Getmallow.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
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 debuggingTime 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.
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 | With Replay CI Agent | |
|---|---|---|
| Test fails | Read error message, guess at cause | Agent traces exact failure sequence |
| Root cause | Manual reproduction, console.logs, trial and error | Identified automatically with confidence score |
| Time to fix | 30 min to 2+ hours per failure | Fix suggestion posted in minutes |
| Flaky tests | Marked as flaky, ignored, accumulate | Each failure investigated individually with runtime evidence |
| Team impact | PRs blocked, CI re-runs burning time and money | Developer reads comment, applies fix, merges |
| Effort | High — requires deep codebase knowledge | Zero — agent does the investigation |
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
Playwright
Cypress
GitHub Actions
CircleCIJenkinsCoding agents
Claude Code
Codex
Cursor
Copilot
WindsurfCommon 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.