Open Editor

First, find the .uproject file in the current working directory:

# Find .uproject file in current directory
dir /b *.uproject

This returns the project file name (e.g., S2.uproject). Use this for all subsequent operations.

Workflow

Step 1: Read Cached Engine Path

Check if the engine path is cached in ./Saved/claude-data.txt:

Read file: {CWD}/Saved/claude-data.txt

Expected format:

[UnrealEngine]
EnginePath={engine.path}
EngineAssociation=5.7.1-huli
LastOpened=2025-12-14T12:00:00

[ProjectInfo]
ProjectName=S2
ProjectPath={CWD}/{ProjectFile}

Step 2: If No Cache, Query Registry

If claude-data.txt doesn't exist or is invalid, query the Windows Registry:

reg query "HKEY_CURRENT_USER\SOFTWARE\Epic Games\Unreal Engine\Builds"

Then read the project file to get the EngineAssociation:

Read file: {CWD}/{ProjectFile}

Extract EngineAssociation field (e.g., 5.7.1-huli) and match it with registry entries.

Step 3: Save Cache

Save the engine path to ./Saved/claude-data.txt:

# Ensure Saved directory exists
mkdir "{CWD}\Saved" 2>nul

Use Write tool to create/update {CWD}/Saved/claude-data.txt with the detected path.

Step 4: Launch Editor

Launch Unreal Editor using the detected path:

start "" "{EnginePath}/Engine/Binaries/Win64/UnrealEditor.exe" "{CWD}\{ProjectFile}"

Step 5: Regenerate Project Files (Optional)

If user requests or if project files are stale, regenerate:

"{EnginePath}/Engine/Binaries/DotNET/UnrealBuildTool/UnrealBuildTool.exe" -projectfiles -project="{CWD}\{ProjectFile}" -game -engine -progress

Or use the batch file if available:

"{EnginePath}/GenerateProjectFiles.bat" "{CWD}\{ProjectFile}"

Implementation Steps

1. Detect Project File

Action: Find .uproject in current directory
Command: dir /b *.uproject (or use Glob tool with pattern "*.uproject")
Result: Store as {ProjectFile} variable

2. Check Cache File

Action: Read {CWD}/Saved/claude-data.txt
- If exists and valid: Extract EnginePath, proceed to Step 5
- If missing or invalid: Proceed to Step 3

3. Auto-Detect Engine

Action: Query registry and read {ProjectFile}
Commands:
1. reg query "HKEY_CURRENT_USER\SOFTWARE\Epic Games\Unreal Engine\Builds"
2. Read {CWD}/{ProjectFile}
3. Match EngineAssociation with registry entry
4. Save result to claude-data.txt

4. Create/Update Cache

Action: Write to {CWD}/Saved/claude-data.txt
Format:
[UnrealEngine]
EnginePath={detected_path}
EngineAssociation={from_uproject}
LastOpened={current_timestamp}

[ProjectInfo]
ProjectName={ProjectName}
ProjectPath={CWD}/{ProjectFile}

5. Launch Editor

Action: Execute launch command
Command: start "" "{EnginePath}/Engine/Binaries/Win64/UnrealEditor.exe" "{CWD}\{ProjectFile}"

6. Regenerate Project (If Requested)

Ask user: "Do you want to regenerate project files?"
Options:
- Yes, regenerate Visual Studio/Rider project files
- No, just open the editor
- Regenerate and open editor

User Interaction

Default Behavior (No Options)

When user invokes open-editor without options:

1. Detect .uproject file in current directory
2. Read or auto-detect engine path
3. Launch editor directly
4. Report status to user

With Regeneration Request

When user asks to regenerate:

1. Run UnrealBuildTool with -projectfiles flag
2. Wait for completion
3. Launch editor

Force Re-detect Engine

When user suspects wrong engine or cache is stale:

1. Delete or ignore claude-data.txt
2. Re-query registry
3. Update cache
4. Launch editor

Error Handling

No .uproject Found

If no .uproject file in current directory:

Error: No .uproject file found in current directory
Solution:
1. Verify you are in the correct project directory
2. Current directory: {CWD}
3. Expected: A directory containing *.uproject file

Engine Not Found

If registry query fails or EngineAssociation not matched:

Error: Could not find Unreal Engine build for association '{EngineAssociation}'
Solution:
1. Verify {ProjectFile} EngineAssociation value
2. Check if custom engine is registered in Epic Games Launcher
3. Manually register engine:
   - Open Epic Games Launcher
   - Settings > Installed Engine Versions
   - Add custom engine path

Editor Fails to Launch

If start command fails:

Error: Failed to launch Unreal Editor
Checks:
1. Verify engine path exists: {EnginePath}/Engine/Binaries/Win64/UnrealEditor.exe
2. Verify project file exists: {CWD}/{ProjectFile}
3. Check for crash logs in: {CWD}/Saved/Crashes

Project File Corruption

If .uproject is corrupted:

Action: Offer to regenerate from template
Warning: This will reset plugin configuration

Example Session

Normal Launch

User: open editor
Assistant:
1. Detecting project file... Found: S2.uproject
2. Reading cached engine path from ./Saved/claude-data.txt...
3. Found: EnginePath={engine.path} (5.7.1-huli)
4. Launching Unreal Editor...
5. Done! Editor is starting.

First Time / Cache Miss

User: open editor
Assistant:
1. Detecting project file... Found: S2.uproject
2. Cache not found, detecting engine...
3. Reading S2.uproject... EngineAssociation: 5.7.1-huli
4. Querying registry... Found: {engine.path}
5. Saving cache to claude-data.txt...
6. Launching Unreal Editor...
7. Done! Editor is starting.

With Regeneration

User: open editor and regenerate project files
Assistant:
1. Detecting project file... Found: S2.uproject
2. Reading cached engine path... Found: {engine.path}
3. Regenerating project files...
4. Running UnrealBuildTool -projectfiles...
5. Project files regenerated successfully!
6. Launching Unreal Editor...
7. Done! Editor is starting.

Cache File Format

Location: {CWD}/Saved/claude-data.txt

Format (INI-style):

[UnrealEngine]
EnginePath={engine.path}
EngineAssociation=5.7.1-huli
LastOpened=2025-12-14T10:30:00

[EditorSettings]
LastMap=/Game/Maps/DevMap
WindowMode=Windowed

[ProjectInfo]
ProjectName=S2
ProjectPath={CWD}/S2.uproject

Commands Reference

Find Project File

dir /b *.uproject

Launch Editor

start "" "{EnginePath}/Engine/Binaries/Win64/UnrealEditor.exe" "{CWD}\{ProjectFile}"

Regenerate Project Files

"{EnginePath}/Engine/Binaries/DotNET/UnrealBuildTool/UnrealBuildTool.exe" -projectfiles -project="{CWD}\{ProjectFile}" -game -engine -progress

Query Registry

reg query "HKEY_CURRENT_USER\SOFTWARE\Epic Games\Unreal Engine\Builds"

Verify Editor Executable

if exist "{EnginePath}/Engine/Binaries/Win64/UnrealEditor.exe" (echo Editor found) else (echo Editor NOT found)

Success Criteria

• Project file detected dynamically from current directory
• Editor launches successfully
• Cache file is created/updated with correct paths
• User receives clear status feedback
• Errors are handled gracefully with actionable solutions

Notes

• This skill is Windows-specific (uses start command and registry queries)
• Engine path uses forward slashes for compatibility
• Project path uses backslashes (Windows native)
• The start "" syntax prevents blocking the terminal
• All paths are resolved relative to the current working directory
• Works with any Unreal project, not just S2

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