Unity Slow Compile and Domain Reload

How to fix it

Try these in order — the most common fix is first.

1. 1. Turn off domain reload for Play mode

   Copy steps
   1. Open Edit > Project Settings > Editor
   2. Enable Enter Play Mode Options
   3. Untick Reload Domain (and optionally Reload Scene)
   4. Reset static variables yourself since they are no longer cleared
   Did this fix it? Yes No

2. 2. Use assembly definition files

   Copy steps
   1. Right-click in Project > Create > Scripting > Assembly Definition
   2. Split stable code (plugins, libraries) from code you edit often
   Did this fix it? Yes No

3. 3. Control Auto Refresh

   Copy steps
   1. Open Edit > Preferences > Asset Pipeline
   2. Set Auto Refresh to Enabled Outside Playmode or Disabled and press Ctrl/Cmd+R to refresh manually
   Did this fix it? Yes No

4. 4. Move the project to an SSD

   Copy steps
   1. Keep the project and Library on a fast SSD
   2. Exclude the project folder from antivirus real-time scanning
   Did this fix it? Yes No

Symptoms

Long 'Compiling scripts' or 'Reloading domain' bars after each edit or when pressing Play, sometimes taking tens of seconds.

Why it happens

• Domain reload and scene reload on every Play mode entry
• One big Assembly-CSharp so every change recompiles everything
• Many Asset Store plugins and large Library
• Slow disk or too little RAM
• Auto Refresh recompiling on each file save

This guide also covers

• unity slow compile
• unity domain reload slow
• unity compiling scripts takes forever
• why is unity so slow

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