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Start by identifying where the failure happens: opening or compiling the project, building the Player, launching it, or running it. A successful Build followed by a failed launch needs a different investigation from a build that never finishes. Record your Unity Editor version, target platform, exact error and relevant log before changing code or upgrading Unity.
First, pinpoint the failing stage
“Won’t build or run” can describe several different problems. Note whether the Unity Editor opens the project, whether it fails while creating a Player, or whether the Player is created but does not start on the selected target. If it starts but performs poorly, that is a runtime performance issue—not a build failure.
- Project import or Editor compile: The project does not open cleanly or scripts fail to compile.
- Player build: Unity cannot complete the build.
- Launch: A Player is created, but it does not start on the target.
- Runtime: The Player starts, but behavior or performance is wrong.
Before troubleshooting, write down the Unity version, target platform, whether the Editor opens the project, the failing stage, and the first relevant error with the surrounding log context. These details help distinguish a target configuration problem from a code or runtime issue.
Check compatibility and target build support
Verify requirements for the exact Unity version
Unity documents Editor requirements separately from the requirements for a built Player. Check the requirements for the project’s precise Editor version and target platform rather than assuming a single set applies to every release. For example, Unity 6.0 lists Windows 10 version 21H1 (build 19043) or newer for the Windows Editor, macOS Big Sur 11 or newer for the macOS Editor, and Ubuntu 22.04 or 24.04 for Linux Editor use. Its requirements page recommends at least 8 GB of RAM for the Editor and notes that project size and complexity can require more. These are Unity 6.0 requirements, not universal minimums for all Unity versions. See Unity 6.0 system requirements.
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Confirm the platform module and any target tools
If the selected platform’s build support module is missing, install it through Unity Hub using the Platform Browser’s install route. Restart the Editor after the module finishes installing. Some targets also require an SDK or toolchain; check the documentation for the exact Unity version and platform you are building for.
Check scenes and build configuration
In the Build Settings window, confirm that the intended scenes appear in Scenes in Build and are enabled, and that the correct target is selected. If the scenes list is empty, add the open scenes. Review the selected platform’s options as well, since build settings vary by target. Unity’s Build command creates the Player; Build and Run creates it and then launches it on the chosen target. Consult Unity’s Build Settings documentation for the version-specific UI and options.
Find the useful error in the right log
Start with the first relevant error, not just the last line displayed after a failure. Keep the surrounding context; a final message may only report that an earlier operation failed. The Unity Console can open the Editor log. Unity also maintains logs for the Package Manager, licensing, development Players and Hub. The location and method for runtime logs depend on the platform.
- Android: Inspect runtime output with logcat.
- WebGL: Inspect the browser’s JavaScript console.
- Windows Player: The log is under
AppDataLocalLowCompanyNameProductNamePlayer.login the user profile. - macOS and Linux: Use the platform-specific user log location documented by Unity.
See Unity’s log files documentation for log types and locations. When asking for help, include the Unity version, target, full first relevant error, and the surrounding Editor or Player log rather than a cropped screenshot of the last message.
Reproduce the build consistently
If the failure is intermittent or needs to be compared across runs, use the same project path and target configuration each time. Unity’s command-line build documentation identifies -projectPath and -quit as required build arguments, and recommends -batchmode, -logFile, and either -buildTarget or -activeBuildProfile. Match the target configuration to the failing build and save the log so you can compare runs. Exact command behavior and available options depend on the Editor version; use Unity’s command-line arguments reference.
Test Editor logic separately from the target Player
Tests can narrow down which stage is broken, but they answer different questions:
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- Edit Mode tests check code that can be exercised in the Editor.
- Play Mode tests check runtime behavior in the Unity environment.
- A target Player test checks behavior on the platform where the build is failing.
A passing Editor test does not prove that a Player will build or launch on a particular target. Check that test assemblies reference the code under test and the required test assemblies. Unity’s Unity Test Framework package documentation covers Edit Mode and Play Mode testing; match setup details to the package and Editor version in the project.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Profile only after the Player launches
If the Player builds and starts but runs slowly, investigate runtime performance rather than treating it as a build problem. Unity’s Profiler can attach to a running Player built with Development Build enabled. It cannot diagnose a build that never completes. See Unity’s Profiler documentation.
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Choose the next step from the evidence
- If the Editor cannot open or compile the project, capture the Editor Console error and Editor log first.
- If the Player build fails, verify target support, requirements, scenes, target selection, and the first relevant build error.
- If the build succeeds but launch fails, inspect the target’s runtime log—especially logcat for Android or the browser console for WebGL.
- If the Player launches but behaves incorrectly, use Play Mode and target Player tests to separate Editor behavior from target-specific behavior.
- If it launches but performs poorly, profile the running Development Build.
Without the project’s Unity version, target platform, complete error output, and relevant logs, there is no reliable way to name one specific fix. Use those details to narrow the failure before changing project settings or code.
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