Unity FBX Import with Full URLs

This skill ensures that when importing external 3D models (FBX files) into Unity using the Unity MCP Unity_ImportExternalModel tool, full and complete URLs are always provided, preventing import failures due to incomplete paths.

When to use this skill

Use this skill automatically whenever:

• Importing FBX files from external sources
• Adding 3D models to the Unity project
• Loading assets from URLs or file paths
• User mentions: "import model", "add FBX", "load 3D asset", "bring in model"
• Using the Unity_ImportExternalModel tool from Unity MCP

Core principle

ALWAYS use complete, fully-qualified URLs for FBX files.

Never use relative paths, partial URLs, or assume path completion. The FbxUrl parameter must be a complete URL or absolute file path.

Instructions

Step 1: Identify the FBX source

When a user requests to import a model, determine the source:

1. Remote URL (HTTP/HTTPS):

• Must start with http:// or https://
• Must include the full domain and path
• Filename must end with .fbx or .zip
• IMPORTANT: Include ALL query parameters and tokens after the extension
• Query parameters (like ?param=value&other=data) are required for authentication
• Example: https://example.com/models/character.fbx?token=abc123&auth=xyz
• Example: https://cdn.fbcdn.net/path/file.fbx?_nc_gid=xxx&_nc_oc=yyy&oh=zzz

1. Local file (file system):

• Must be an absolute path (not relative)
• Windows: C:/Users/name/Downloads/model.fbx
• Unix/Mac: /home/user/models/model.fbx
• Must end with .fbx or .zip

1. ZIP archive:

• Can be URL or local path
• Must contain an FBX file inside
• Example: https://example.com/assets.zip

Step 2: Validate the URL format

Before calling Unity_ImportExternalModel, verify the URL:

CRITICAL: For URLs with query parameters (like ?token=...&auth=...), you MUST include the ENTIRE URL including all parameters. Query parameters often contain authentication tokens required for download.

Valid examples:

• https://cdn.example.com/assets/models/chair.fbx
• https://cdn.example.com/models/chair.fbx?token=abc123&auth=xyz789 (with query params)
• https://scontent.fbcdn.net/model.fbx?_nc_gid=xxx&_nc_oc=yyy&oh=zzz (Meta CDN with auth)
• http://localhost:8000/models/character.fbx
• file:///C:/Users/name/Downloads/robot.fbx
• C:/Projects/Models/tree.fbx (Windows absolute)
• /home/user/assets/car.fbx (Unix absolute)
• https://github.com/user/repo/releases/download/v1.0/model.zip

Invalid examples (never use these):

• models/chair.fbx (relative path)
• ~/Downloads/robot.fbx (tilde expansion not supported)
• example.com/model.fbx (missing protocol)
• ../assets/model.fbx (relative path)
• model.fbx (no path at all)

Step 3: Get required parameters

The Unity_ImportExternalModel tool requires:

1. Name (required):

• Simple identifier (single word, no spaces)
• Use alphanumeric characters and underscores/hyphens
• Example: office_chair, character_01, tree_oak

1. FbxUrl (required):

• MUST be a complete, full URL or absolute path
• No relative paths allowed
• Include protocol for remote URLs (http://, https://)

1. Height (required):

• Desired height in Unity units (meters)
• Reasonable values: 0.1 to 10.0 for most objects
• Example: 1.8 for human-sized character, 2.0 for chair

1. AlbedoTextureUrl (optional):

• Full URL to texture file (same rules as FbxUrl)
• Can be local file or remote URL
• Common formats: .png, .jpg, .jpeg

Step 4: Call Unity_ImportExternalModel with full URL

Use the Unity MCP tool with complete parameters:

{
  "Name": "office_chair",
  "FbxUrl": "https://example.com/models/office_chair.fbx",
  "Height": 1.0,
  "AlbedoTextureUrl": "https://example.com/textures/chair_diffuse.png"
}

Never omit the protocol or use partial paths.

Step 5: Handle the import result

After calling Unity_ImportExternalModel:

1. Check for success:

• Tool returns success: true if import succeeded
• Result includes GameObject and Prefab information
• Note the bounds (size and center) for placement

1. Extract important data:

• GameObject instance ID and name
• Prefab path for reuse
• World size and center (for placement operations)

1. Report to user:

• Confirm successful import
• Show the GameObject name and prefab path
• Mention the size and position
• Suggest next steps (placement, scaling, etc.)

Step 6: Use with unity-placement skill

After importing, use the bounds information with the unity-placement skill for proper positioning:

The imported model has:
- Size: [width, height, depth]
- Center: [x, y, z]
- Prefab: Assets/Prefabs/name.prefab

Consider the size when placing relative to other objects.

Handling user-provided paths

If user provides a partial path

When the user gives an incomplete path, ask for the complete path:

User: "Import models/car.fbx"

Ask for clarification: "I need the complete path to the FBX file. Is it:

• A remote URL? (e.g., https://example.com/models/car.fbx)
• A local file? Please provide the absolute path (e.g., C:/Projects/models/car.fbx)

What is the full path to car.fbx?"

If user provides a URL without protocol

User: "Import from example.com/models/chair.fbx"

Clarify the protocol: "Should this be:

• https://example.com/models/chair.fbx (HTTPS)
• http://example.com/models/chair.fbx (HTTP)

Which protocol should I use?"

If user provides a relative path

User: "Import ../models/tree.fbx"

Request absolute path: "Relative paths aren't supported. Please provide the absolute path to tree.fbx.

For example:

• Windows: C:/Projects/models/tree.fbx
• Mac/Linux: /home/user/projects/models/tree.fbx

What is the full path?"

Best practices

1. Always verify URL format before calling Unity_ImportExternalModel
2. Never assume paths - always use what's explicitly provided or ask for clarification
3. Prefer absolute paths over any form of relative path
4. Include protocol for all remote URLs (http://, https://)
5. Validate file extension - must be .fbx or .zip
6. Use simple names - alphanumeric with underscores/hyphens only
7. Set reasonable heights - 0.1 to 10.0 for most objects
8. Check import results - verify success and extract bounds data
9. Coordinate with unity-placement - use bounds for subsequent positioning

Error prevention checklist

Before calling Unity_ImportExternalModel, verify:

• [ ] FbxUrl is a complete URL or absolute path
• [ ] URL includes protocol if remote (http:// or https://)
• [ ] ALL query parameters are included (everything after ? in the URL)
• [ ] Path is absolute if local (starts with C:/ or /)
• [ ] No relative path components (no ../ or ./)
• [ ] No tilde expansion (no ~/)
• [ ] Filename ends with .fbx or .zip (query params can follow)
• [ ] Name parameter is a simple identifier (no spaces)
• [ ] Height is a reasonable positive number
• [ ] AlbedoTextureUrl (if provided) is also a full URL/path with all params

Fallback: When Unity_ImportExternalModel is unavailable

If Unity_ImportExternalModel is not available but other Unity MCP tools (like Unity_RunCommand) are working, there are two options.

Option A: Enable the tool in Unity

Tell the user:

"The Unity_ImportExternalModel tool is not currently enabled. To enable it:

1. In Unity, go to Project Settings -> AI -> Unity MCP Server
2. Under the Core section, toggle on Unity_ImportExternalModel
3. The tool will become available immediately — no restart needed."

Option B: Manual import via Unity_RunCommand

If the user cannot or does not want to enable the tool, read FALLBACK_MANUAL_IMPORT.md (next to this file) for a step-by-step guide to replicate the import pipeline using Unity_RunCommand, based on the reference implementation in the com.unity.ai.assistant package.

Quick reference

Required format for FbxUrl

Integration with other skills

With unity-placement

After importing, use the returned bounds with unity-placement:

Imported model "robot_character":
- Size: [0.6, 1.8, 0.4]
- Center: [0, 0.9, 0]
- Prefab: Assets/Prefabs/robot_character.prefab

To place this robot on the platform:
[Use unity-placement skill with the size data]

Remember

The Unity MCP Unity_ImportExternalModel tool requires complete, absolute URLs or paths. When in doubt:

1. Ask the user for the complete path
2. Verify the URL format before calling the tool
3. Include the protocol for remote URLs
4. Use absolute paths for local files
5. Never guess or auto-complete partial paths
6. Never use relative paths or tilde expansion

Goal: Prevent import failures by ensuring every FbxUrl parameter is a valid, complete, fully-qualified URL or absolute file path.