Langserve

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LangServe helps developers deploy LangChain runnables and chains as a REST API, automatically inferring input/output schemas and providing API documentation. It integrates with FastAPI and offers client SDKs for easy interaction.

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At a glance

Pricing

Open Source

Free tier

Yes

API

Yes

Skill level

Technical

About

What is langserve?

LangServe is a tool designed for developers to deploy LangChain runnables and chains as a REST API. It leverages FastAPI and Pydantic for robust data validation and automatic inference of input and output schemas. Key features include efficient /invoke, /batch, and /stream endpoints for handling concurrent requests, along with /stream_log and /stream_events for detailed streaming of intermediate steps. LangServe also provides an interactive playground at /playground/ for testing runnables with streaming output and tracing to LangSmith. While it offers a client SDK for Python and JavaScript, for new projects, the LangGraph Platform is recommended, as LangServe will primarily focus on bug fixes rather than new feature development.

Best used for

Ideal for developers who need to expose LangChain runnables and chains as REST APIs, integrate AI models into applications, and provide interactive playgrounds for testing. Especially valuable for those building on the LangChain ecosystem who require robust API deployment with automatic schema validation and streaming capabilities.

Common actions

deploy AI models

create REST APIs

integrate LangChain

stream AI outputs

face swapping"AI Agents"github copilotopen-sourcedeepfakelow-code/no-codeautomated workflowcollaborationworkflows

Capabilities

Key features

Deploy LangChain runnables
Automatic schema inference
REST API endpoints
Stream intermediate steps
Built-in tracing to LangSmith
Interactive playground
Python/JavaScript client SDK

Target Audience

developer

Integrations

fastapilangchainlangsmith

Pricing & Plans

Open Source

Free

FAQs

What is the recommended platform for new projects involving LangGraph?

For new projects, especially those involving LangGraph, the LangGraph Platform is recommended over LangServe. LangServe will continue to receive bug fixes but will not accept new feature contributions.

Does LangServe support streaming intermediate steps from a chain or agent?

Yes, LangServe provides /stream_log and /stream_events endpoints. These allow you to stream all or some intermediate steps from your LangChain chain or agent as they are generated, offering detailed insights into the process.

Can I use LangServe with Pydantic V2?

Versions of LangServe prior to 0.3.0 had issues generating OpenAPI docs with Pydantic V2 due to FastAPI limitations. It is recommended to upgrade to LangServe 0.3.0 or later for proper Pydantic V2 compatibility.

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Also listed in

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AI Agents & Automation › AI Frameworks & Infra

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