How I Manage Long Compile Times in Unity

How I Manage Long Compile Times in Unity

Unity's script compilation can be painfully slow in large projects, and it can seriously disrupt workflow and developer momentum. In my case, with a fairly large project, full domain reloads were taking 30–45 seconds on average. Interestingly, compilation for changes in certain assemblies was relatively quick (3–5 seconds), but other parts of the domain reload process were dragging things down.



⚠️ Note: This post focuses specifically on script compile times in the Unity Editor, including domain reload and reflection delays that occur after code changes. It does not cover strategies for runtime build optimization (e.g., IL2CPP or build pipeline tweaks), nor does it address the time it takes to enter play mode.

Here are a few strategies I use to keep compile and iteration times manageable:

☠️ InitializeOnLoad Can Be Death by a Thousand Cuts

While InitializeOnLoad callbacks and similar can be lightweight individually, they can add up quickly — especially in large projects that include a lot of third-party assets. Each little callback might only cost a fraction of a second, but when you're dealing with dozens or hundreds of them, it becomes noticeable.



Tips:

  • Audit and reduce your use of InitializeOnLoad and similar editor callbacks.

  • Be selective about third-party assets and packages — many bring hidden callbacks with them.

  • Unused built-in packages like Cinemachine, Timeline, etc., may also include InitializeOnLoad usage. Remove what you don’t use.

📦 Use Addressables

Unity’s Addressables system can help both at runtime and in the editor:

  • It decouples asset dependencies, which can reduce domain reload overhead.

  • It gives you more control over when and how assets are loaded.

The setup has a bit of a learning curve, but it pays off — especially in large projects with many assets.

🔥 Hot Reloading

There’s a great third-party tool that enables code hot reloading without full recompilation:

🔗 Hot Reload – Unity Asset Store

While I haven’t fully adopted it in production yet — it uses some kind of code injection which makes me a bit wary — it could be a game-changer for iteration speed during prototyping or smaller projects.

📐 Assembly Definitions (AsmDefs)

Assembly Definitions are essential for managing compile time in Unity:

  • Keep a clean and logical dependency graph.

  • Wrap third-party code in AsmDefs if they aren’t already.

  • Modularize your project. For example:

    • My Sys assembly is atomic — it has no dependencies.

    • My InfluenceMap assembly only references Sys and Core.

Also, disabling automatic compilation on code changes can improve iteration flow:

  • You can continue inspecting the editor while making changes.

  • You can rerun the game before recompiling, which speeds up debugging and testing.

📊 Track Compile Times with This Tool

Here’s a great open-source tool that helps visualize Unity's compilation process:

🔗 Compilation Visualizer – GitHub

It gives you:

  • A breakdown of what’s being recompiled.

  • How long each phase takes.

  • A baseline to monitor when your editor is bogging down and may need a restart.

It’s an essential tool in my toolbox for keeping an eye on performance drift over time.







🧠 Unity Profiler

Don’t forget the Unity Profiler. It can actually give you timing data for script compilation and domain reload.

Use it to:

  • Spot unexpected spikes or delays.

  • Validate whether optimizations are actually helping.

  • Identify bottlenecks you might not expect (like asset processing during domain reload).





🧹 Keep the Project Tidy

Having unused code and assets lying around doesn’t just clutter your project — it can slow things down:

  • While it doesn’t drastically affect raw compile times,

  • It does impact the Reload Domain phase — Unity still has to scan and register everything.


This tool helped me clean up abandoned assets:

🔗 Unity Dependencies Hunter – GitHub

Unused code can also increase compile time unnecessarily. Even though script compilation times were fine for me, trimming dead code might save you more time depending on your project structure.




Final Thoughts

Unity still has a long way to go in terms of making large projects feel fast and responsive during iteration. But with the right habits and tooling, it’s absolutely possible to reclaim your development flow.

These strategies helped me reduce waiting time and keep the iteration loop snappy. I hope they help you too!