Architecture

Open LangGraph Server bridges the gap between LangGraph workflows and web applications, providing a standardized API layer that enables seamless integration across different JavaScript frameworks.

Core Architecture

Open LangGraph Server uses a three-layer architecture built on standard Web APIs, making it framework-agnostic and portable:

Key Components

Framework Adapters (Thin Wrappers)

Lightweight adapters that bridge framework-specific APIs to the standard fetch handler:

• Next.js Adapter: Extracts context from x-langgraph-context header and handles Next.js initialization patterns
• Hono.js Adapter: Extracts context from Hono's langgraph_context variable
• Standard Fetch Handler: Core implementation works directly on any platform supporting Web APIs

All adapters share the same core implementation, ensuring:

• Consistent behavior across platforms
• Single source of truth for API logic
• Easy migration between frameworks

Core Fetch Handler (Standard Web APIs)

Platform-agnostic implementation using only standard Request/Response APIs:

• Route Matching: Regex-based routing without framework dependencies
• Request Validation: Zod-based runtime validation
• SSE Streaming: Custom SSE implementation with heartbeat support
• Context Management: Framework-agnostic context passing

Works on:

• Cloudflare Workers
• Deno Deploy
• Vercel Edge Functions
• Bun
• Any platform with standard fetch APIs

API Abstraction Layer

Implements LangGraph SDK-compatible REST endpoints with streaming support:

• Assistants API: Graph discovery and metadata management
• Threads API: Conversation lifecycle and state management
• Runs API: Graph execution with real-time streaming results
• Type Safety: Runtime validation using Zod schemas

Storage & Persistence Layer

Flexible storage backends for different deployment scenarios:

• Checkpoint Storage: Persists graph state across executions (SQLite/PostgreSQL/Redis/Memory)
• Message Queues: Handles real-time streaming data with automatic backend selection
• Thread Management: Coordinates conversation lifecycles and metadata

Data Flow

Configuration Philosophy

Open LangGraph Server embraces "convention over configuration" with environment-based setup:

• Automatic Backend Selection: Chooses storage based on available environment variables
• Sensible Defaults: Works out-of-the-box with memory storage for development
• Progressive Enhancement: Add databases and queues as needs grow

Design Principles

• Platform Agnostic: Core implementation uses only standard Web APIs (Request/Response)
• Framework Neutral: Thin adapters make framework integration effortless
• Type Safe: Full TypeScript support with Zod runtime validation
• Production Ready: Built-in scalability, monitoring, and error handling
• Developer Friendly: Simple APIs with comprehensive documentation
• Easy Migration: Switch platforms without rewriting API logic

Why This Architecture?

Single Source of Truth

All framework adapters use the same core implementation, meaning:

• Bug fixes apply everywhere instantly
• New features available to all platforms
• Consistent behavior across deployments

Maximum Portability

Based on Web Standards (WHATWG Fetch API):

• Run on Cloudflare Workers, Deno Deploy, Vercel Edge
• No framework lock-in
• Future-proof as standards evolve

Minimal Overhead

Framework adapters are just thin wrappers:

• Hono adapter: ~30 lines of code
• Next.js adapter: ~40 lines of code
• Direct fetch usage: 0 lines of adapter code