diff --git a/pyproject.toml b/pyproject.toml
index 7eccb2bb1..e360ebdb6 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -105,6 +105,7 @@ test = [
   "pytest-mock>=3.14.0",
   "pytest-xdist>=3.6.1",
   "pytest>=8.3.4",
+  "python-multipart>=0.0.9",
   # go/keep-sorted end
 ]
 
diff --git a/src/google/adk/cli/fast_api.py b/src/google/adk/cli/fast_api.py
index 2e37f3bb1..face2495e 100644
--- a/src/google/adk/cli/fast_api.py
+++ b/src/google/adk/cli/fast_api.py
@@ -20,6 +20,7 @@
 import logging
 import os
 from pathlib import Path
+import shutil
 import time
 import traceback
 import typing
@@ -32,6 +33,7 @@
 from fastapi import FastAPI
 from fastapi import HTTPException
 from fastapi import Query
+from fastapi import UploadFile
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import RedirectResponse
 from fastapi.responses import StreamingResponse
@@ -51,7 +53,6 @@
 from typing_extensions import override
 from watchdog.events import FileSystemEventHandler
 from watchdog.observers import Observer
-import yaml
 
 from ..agents import RunConfig
 from ..agents.live_request_queue import LiveRequest
@@ -212,14 +213,6 @@ class GetEventGraphResult(common.BaseModel):
   dot_src: str
 
 
-class AgentBuildRequest(common.BaseModel):
-  agent_name: str
-  agent_type: str
-  model: str
-  description: str
-  instruction: str
-
-
 def get_fast_api_app(
     *,
     agents_dir: str,
@@ -820,26 +813,30 @@ async def delete_artifact(
 
   @working_in_progress("builder_save is not ready for use.")
   @app.post("/builder/save", response_model_exclude_none=True)
-  async def builder_build(req: AgentBuildRequest):
+  async def builder_build(files: list[UploadFile]) -> bool:
     base_path = Path.cwd() / agents_dir
-    agent = {
-        "agent_class": req.agent_type,
-        "name": req.agent_name,
-        "model": req.model,
-        "description": req.description,
-        "instruction": f"""{req.instruction}""",
-    }
-    try:
-      agent_dir = os.path.join(base_path, req.agent_name)
-      os.makedirs(agent_dir, exist_ok=True)
-      file_path = os.path.join(agent_dir, "root_agent.yaml")
-      with open(file_path, "w") as file:
-        yaml.dump(agent, file, default_flow_style=False)
-      agent_loader.load_agent(agent_name=req.agent_name)
-      return True
-    except Exception as e:
-      logger.exception("Error in builder_build: %s", e)
-      return False
+
+    for file in files:
+      try:
+        # File name format: {app_name}/{agent_name}.yaml
+        if not file.filename:
+          logger.exception("Agent name is missing in the input files")
+          return False
+
+        agent_name, filename = file.filename.split("/")
+
+        agent_dir = os.path.join(base_path, agent_name)
+        os.makedirs(agent_dir, exist_ok=True)
+        file_path = os.path.join(agent_dir, filename)
+
+        with open(file_path, "w") as buffer:
+          shutil.copyfileobj(file.file, buffer)
+
+      except Exception as e:
+        logger.exception("Error in builder_build: %s", e)
+        return False
+
+    return True
 
   @app.post("/run", response_model_exclude_none=True)
   async def agent_run(req: AgentRunRequest) -> list[Event]: