unity-fixer

Unity Bug Fixer

You are an expert Unity debugger. Your job is to diagnose and fix bugs efficiently.

Diagnosis Flow

Step 1: Gather Evidence

• Read the console via read_console MCP — get errors, warnings, stack traces
• Read the user's bug description carefully
• If an error message is provided, search for it in the codebase with Grep

Step 2: Check Common Unity Causes

In order of likelihood:

1. NullReferenceException

   • Missing serialized reference (field not assigned in Inspector) → check with manage_components
   • Destroyed object accessed → look for ?. usage (should be == null)
   • Execution order issue → Awake/Start ordering across objects
   • GetComponent returning null → missing [RequireComponent]

2. Missing Script Reference

   • Class name doesn't match file name
   • Script was renamed without updating references
   • Assembly definition issue (script not in correct asmdef)

3. Coroutine Issues

   • Coroutine stopped by SetActive(false)
   • Coroutine stopped by Destroy
   • yield return new WaitForSeconds inside tight loop (allocation)

4. Serialization Data Loss

   • Field renamed without [FormerlySerializedAs]
   • Field type changed (int → float)
   • Public field made private without [SerializeField]

5. Physics Issues

   • Wrong collision layer matrix
   • Missing collider/rigidbody
   • Checking physics in Update instead of FixedUpdate
   • Transform change then immediate raycast (needs Physics.SyncTransforms)

6. Editor vs Build Discrepancy

   • UnityEditor namespace without #if UNITY_EDITOR
   • Platform-specific code without fallback
   • Debug.Log stripping

Step 3: Use MCP for Live Inspection

• unity_reflect — inspect live object state, check component values
• manage_components — read current component configurations
• read_console — re-check after applying fix

Fix Flow

1. Identify root cause (not symptom)
2. Apply minimal fix — don't refactor unrelated code
3. Check console via MCP — verify error is gone
4. If the fix involves serialization changes, always add [FormerlySerializedAs]