diff --git a/apps/api/src/api/tool_instances.py b/apps/api/src/api/tool_instances.py
index 1d5f9ba..769665a 100644
--- a/apps/api/src/api/tool_instances.py
+++ b/apps/api/src/api/tool_instances.py
@@ -1,9 +1,12 @@
 """Tool instance API endpoints."""
 
+import logging
 import os
 import uuid
 from datetime import datetime
 
+logger = logging.getLogger(__name__)
+
 from fastapi import APIRouter, Depends, HTTPException, status
 from pydantic import BaseModel, Field
 from sqlalchemy import select
@@ -33,6 +36,8 @@ router = APIRouter(prefix="/projects", tags=["tool-instances"])
 class CreateInstanceRequest(BaseModel):
     """Request body for creating a tool instance."""
 
+    model_config = {"extra": "ignore"}
+
     tool_type_id: str = Field(description="UUID of the tool type to instantiate")
     display_name: str | None = Field(default=None, description="Optional display name for the instance")
 
@@ -96,6 +101,13 @@ async def create_instance(
     Returns:
         Dictionary with instance details.
     """
+    logger.info(
+        "Creating instance: project_id=%s, repo_id=%s, tool_type_id=%s, display_name=%s",
+        project_id,
+        repo_id,
+        data.tool_type_id,
+        data.display_name,
+    )
     _user = await _get_user(session, user_id)
     _project = await _get_owned_project(project_id, user_id, session)
 
diff --git a/apps/api/src/main.py b/apps/api/src/main.py
index f5ca7dc..412b36c 100644
--- a/apps/api/src/main.py
+++ b/apps/api/src/main.py
@@ -1,8 +1,10 @@
 import logging
 import os
 
-from fastapi import FastAPI
+from fastapi import FastAPI, Request
+from fastapi.exceptions import RequestValidationError
 from fastapi.middleware.cors import CORSMiddleware
+from fastapi.responses import JSONResponse
 from fastapi.staticfiles import StaticFiles
 from sqlalchemy import select, text
 
@@ -48,6 +50,22 @@ app.add_middleware(RequestLoggingMiddleware)
 app.add_middleware(ExceptionLoggingMiddleware)
 
 
+@app.exception_handler(RequestValidationError)
+async def validation_exception_handler(request: Request, exc: RequestValidationError):
+    """Log validation errors and return detailed response."""
+    errors = exc.errors()
+    logger.warning(
+        "Validation error for %s %s: %s",
+        request.method,
+        request.url.path,
+        errors,
+    )
+    return JSONResponse(
+        status_code=422,
+        content={"detail": errors},
+    )
+
+
 async def _table_exists(session, table_name: str) -> bool:
     """Check if a table exists in the database."""
     try: