LangServe: Deploy LangChain Chains as Production-Ready REST APIs
Deploy any LangChain runnable as a REST API with LangServe — automatic endpoints, streaming, validation, and a built-in playground.
What Is LangServe?
LangServe is an official tool from the LangChain ecosystem that lets you deploy any LangChain runnable or chain as a REST API with minimal effort. Built on top of FastAPI and pydantic, it automatically generates OpenAPI-compliant endpoints, input/output schemas, and interactive API documentation from your existing LangChain code.
Whether you are building a question-answering bot over documents (RAG), a multi-step agent workflow, or a simple prompt chain, LangServe turns it into a production-ready API endpoint in minutes. It handles serialization, validation, async streaming, and error handling out of the box.
Key Features
Automatic API Generation
LangServe introspects your LangChain runnable and automatically generates the appropriate REST endpoints. You get POST routes for invocation, streaming via Server-Sent Events (SSE), and batch processing without writing a single route handler.
Built-in Playground UI
LangServe comes with an interactive Playground web UI where you can test your deployed chains directly in the browser. The Playground lets you tweak inputs, inspect outputs, and visualize streaming responses in real time.
Schema Validation
Every endpoint is backed by pydantic models, so inputs and outputs are validated automatically. The generated OpenAPI schema integrates seamlessly with Swagger UI and Postman.
Client Libraries
LangServe provides both a Python client and a JavaScript client for calling deployed APIs. These handle authentication, streaming, error handling, and type conversion.
Quick Start
pip install langserve
from langchain.chains import LLMChain
from langserve import add_routes
from fastapi import FastAPI
app = FastAPI()
add_routes(app, chain, path="/chat")
import uvicorn
uvicorn.run(app, host="0.0.0.0", port=8080)Why Self-Host LangServe?
Self-hosting LangServe gives you full control over your LangChain API deployments. Run it behind your own authentication, scale with your own infrastructure, and keep your data private. Since it is built on FastAPI, it integrates with your existing Docker or cloud-native stack.
Conclusion
LangServe remains one of the easiest ways to expose LangChain chains as APIs. While the LangGraph Platform is the recommended path for new projects, LangServe is still fully functional and widely used in production. It is ideal for teams wanting a lightweight, FastAPI-native solution for deploying LangChain runnables.