Unlogged – open-source record and replay for Java
Hello HN! Parth, and Shardul here. We have been building unlogged.io for the last 21 months. We started as a time travel debugger and pivoted to record and replay with assertions, mocking, and code coverage. You can save the replays in the form of a JSON and commit them to your git. Both Parth and I come from an e-commerce/payments background where production bugs meant heavy financial losses. Big billion days/Black Friday sales meant months of code freezes with low productivity. Before committing the code, we wanted to replay production traffic and know the breaking changes right…
In plain words
Unlogged is an open-source record and replay tool for Java that captures code execution and allows developers to replay production traffic with assertions, mocking, and code coverage analysis. It works through an SDK that adds compile-time probes to log execution details, with replays saved as JSON files that can be committed to Git. Designed for teams building e-commerce and payment systems where production bugs carry significant financial risk, it helps identify breaking changes before deployment.
written from the facts on this page · September 2026
From the sources
In the maker’s words, at launch
Hello HN! Parth, and Shardul here. We have been building unlogged.io for the last 21 months. We started as a time travel debugger and pivoted to record and replay with assertions, mocking, and code coverage. You can save the replays in the form of a JSON and commit them to your git. Both Parth and I come from an e-commerce/payments background where production bugs meant heavy financial losses. Big billion days/Black Friday sales meant months of code freezes with low productivity. Before committing the code, we wanted to replay production traffic and know the breaking changes right away, like in sub-second. Kind of like unit+integration tests on steroids. So, we built an SDK that adds probes to the code in compile time. The SDK logs code execution, in detail. Git: https://github.com/unloggedio/unlogged-sdk We also built an IDE plugin that keeps monitoring code changes, hot reloads these changes, replays the relevant methods, and alerts on failing replays. It also lets developers call Java methods directly, mock downstream methods in run time, highlight code coverage in real-time, and show performance numbers for methods with inlay hints. (right above each method) Git: https://github.com/unloggedio/intellij-java-plugin We are excited to launch the first version of our product that replays with assertions + mocking + code coverage reports right inside the IDE. Link to our IntelliJ plugin: https://plugins.jetbrains.com/plugin/18529-unlogged/ Record and Replay Demo: https://www.youtube.com/watch?v=muCyE-doEB0 Define Assertions on Replay: https://www.youtube.com/watch?v=YKsi1p634-M Track Code Coverage: https://www.youtube.com/watch?v=NMmp954kfaU Generate JUnit Test Cases: https://www.youtube.com/watch?v=rTUmg5b1Z_Q Mocking when replaying: https://www.youtube.com/watch?v=O_aqU1u-Kmw Documentation: http://read.unlogged.io/ Roadmap: 1. Create a production logger -So that the performance impact is minimal -out of the box masking PII from production logs -creating meaningful input/return value combinations from production traffic to be replayed locally. 2. Creating a CI test runner that can integrate with CI/CD pipelines. 3. Auto-Replaying API endpoints of only the changed code. 4. Real-time alerts for the performance impact of code changes. 5. Creating a dashboard with reports, email/slack alerts.
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