Production-ready fullstack template showing how to wire a Python ADK backend to a modern Next.js frontend with streaming responses, local development, and deployment paths to Vertex AI Agent Engine and Vercel.

This repo contains:

• Backend: Python app using Google ADK to run a goal-planning LLM agent
• Frontend: Next.js app with a chat UI, activity timeline, and SSE streaming
• Make targets and scripts to run locally and deploy

Prerequisites:

• Python 3.10–3.12
• Node.js 18+ (recommended: LTS)
• uv (installed automatically by Makefile if missing)
• Google Cloud SDK for cloud deployment

Setup and run locally (backend + frontend):

make install
cp app/.env.example app/.env  # if present, otherwise see Backend env below
make dev

By default the frontend runs at http://localhost:3000 and proxies chat requests to the local ADK backend at http://127.0.0.1:8000 via nextjs/src/app/api/run_sse/route.ts.

• Goal-planning LLM agent powered by Google ADK (app/agent.py)
• Environment-driven routing to either local backend or Vertex AI Agent Engine
• Robust SSE pipeline with JSON-fragment processing for Agent Engine
• Chat UI with message list, streaming content, and activity timeline
• Health checks and helpful error formatting

• Backend: Python, google-adk, vertexai, python-dotenv
• Frontend: Next.js 15, React 19, TailwindCSS, shadcn/ui
• Tooling: uv for Python deps, ESLint + Jest for the frontend, Ruff + Mypy for backend linting/type-checking

app/                       # Python ADK backend
  agent.py                 # Root agent definition (goal-planning)
  agent_engine_app.py      # Deployment helper for Vertex AI Agent Engine
  config.py                # Env loading, Vertex init, deployment config
  utils/                   # GCS + tracing helpers

nextjs/                    # Next.js frontend
  src/app/api/health       # Proxies health checks to backend
  src/app/api/run_sse      # Streaming endpoint (local or Agent Engine)
  src/lib/config.ts        # Env detection + endpoint resolution
  src/lib/handlers/        # Streaming handlers (local/agent-engine)
  src/components/chat/     # Chat UI and timeline components

Makefile                   # install/dev/lint + Agent Engine deploy helper
pyproject.toml             # Python deps and linters

app/agent.py defines an ADK LlmAgent with built-in planning enabled. It accepts a high-level goal and produces a structured plan and execution steps. The model defaults to gemini-2.5-flash and can be changed via env.

Create app/.env with at least the following for local development and deployment:

# Required
GOOGLE_CLOUD_PROJECT=your-gcp-project-id
GOOGLE_CLOUD_LOCATION=us-central1

# Staging bucket for Vertex AI/Agent Engine packaging
# Provide a valid bucket identifier. Example: my-staging-bucket
# (Do not include gs:// prefix.)
GOOGLE_CLOUD_STAGING_BUCKET=my-staging-bucket

# Optional
MODEL=gemini-2.5-flash
AGENT_NAME=goal-planning-agent
EXTRA_PACKAGES=./app
REQUIREMENTS_FILE=.requirements.txt

Notes:

• Configuration is validated at import time in app/config.py and initializes Vertex AI.
• The Makefile’s deploy target will generate .requirements.txt for Agent Engine using uv export.

The Makefile starts the ADK API server for you:

make dev-backend
# or run both backend and frontend together
make dev

This uses uv run adk api_server app --allow_origins="*" which serves the ADK HTTP API at http://127.0.0.1:8000.

Create nextjs/.env.local:

Local backend (default):

BACKEND_URL=http://127.0.0.1:8000
NODE_ENV=development

Agent Engine (direct streaming):

AGENT_ENGINE_ENDPOINT=https://us-central1-aiplatform.googleapis.com/v1/projects/your-project/locations/us-central1/reasoningEngines/YOUR_ENGINE_ID

# Required when calling Agent Engine directly (e.g. Vercel):
# Base64-encoded service account JSON with permissions for Agent Engine
GOOGLE_SERVICE_ACCOUNT_KEY_BASE64=eyJ0eXAiOiJKV1QiLCJh...  # base64 JSON

NODE_ENV=production

Cloud Run (if you host your own proxy backend):

CLOUD_RUN_SERVICE_URL=https://your-service-url.a.run.app
NODE_ENV=production

The frontend auto-detects the deployment mode in nextjs/src/lib/config.ts and will:

• Use Agent Engine when AGENT_ENGINE_ENDPOINT is set
• Use Cloud Run when CLOUD_RUN_SERVICE_URL (or Cloud env vars) are present
• Default to local backend otherwise

npm --prefix nextjs install
npm --prefix nextjs run dev

Open http://localhost:3000.

• API route nextjs/src/app/api/run_sse/route.ts orchestrates streaming and delegates to:
  • run-sse-local-backend-handler.ts for local ADK backend
  • run-sse-agent-engine-handler.ts when using Agent Engine
• For Agent Engine, JSON fragments are transformed into SSE format on the server so the UI can render incremental text and thought parts consistently.

Python (from repo root):

make lint

Node/TypeScript (from repo root):

npm --prefix nextjs run lint
npm --prefix nextjs run test

Tip: Prefer linting and type-checking for fast feedback during development instead of full builds.

Prerequisites:

• gcloud auth application-default login
• gcloud config set project YOUR_PROJECT_ID
• A GCS bucket for packaging (match GOOGLE_CLOUD_STAGING_BUCKET in app/.env)

Deploy:

make deploy-adk

What it does:

• Exports Python dependencies to .requirements.txt using uv
• Packages and deploys the ADK app via app/agent_engine_app.py
• Creates a logs/data bucket for artifacts if missing
• Outputs deployment metadata to logs/deployment_metadata.json

After deployment, set AGENT_ENGINE_ENDPOINT in nextjs/.env.local with the returned Reasoning Engine endpoint to stream from Agent Engine directly.

Use NEXTJS_VERCEL_DEPLOYMENT_GUIDE.md for step-by-step instructions. In short:

• Set environment variables in Vercel (at minimum AGENT_ENGINE_ENDPOINT and GOOGLE_SERVICE_ACCOUNT_KEY_BASE64 if using Agent Engine)
• Push your repo and import the nextjs app into Vercel

GET /api/health on the frontend forwards to the backend health endpoint (/health). Configure backend URL/endpoint via env as described above.

• Missing Google Cloud envs: app/config.py validates env on import. Ensure GOOGLE_CLOUD_PROJECT, GOOGLE_CLOUD_LOCATION, and GOOGLE_CLOUD_STAGING_BUCKET are set in app/.env.
• Authentication for Agent Engine from the frontend requires GOOGLE_SERVICE_ACCOUNT_KEY_BASE64 with correct scopes.
• Local streaming issues: verify BACKEND_URL in nextjs/.env.local and that make dev-backend is running.

Apache-2.0 (unless noted otherwise in third-party files).