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patterns-ai-core/langchainrb

A Ruby library for building LLM-powered applications, offering a unified interface to many LLM providers, vector databases, RAG pipelines and assistants.

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What is it?

Langchain.rb is a Ruby gem for building applications on top of large language models. It gives Ruby developers one interface to call providers such as OpenAI, Anthropic, Google Gemini, Mistral AI, Ollama and AWS Bedrock, so switching backends mostly means changing the class you instantiate.

The library covers the common building blocks of LLM apps: prompt templates, output parsers that turn model text into structured JSON, and retrieval-augmented generation (RAG) over a range of vector search databases including Chroma, Pinecone, Pgvector, Qdrant, Weaviate, Milvus and Elasticsearch. It can load and index files in formats such as PDF, DOCX, CSV and XLSX.

For agent-style use cases, the Assistant class combines an LLM with tools such as a calculator, SQL database access, web search and a file system tool, and supports custom tools. A RAGAS-based evaluation module scores faithfulness, context relevance and answer relevance of RAG pipelines. Optional gems are required for each integration, so applications only pull in what they use.

Key features

  • 01Unified interface for multiple LLM providers, including embeddings, completions and chat
  • 02Vector search integrations with eight databases such as Chroma, Qdrant and Pgvector
  • 03Prompt templates and output parsers that produce structured JSON with automatic fixing
  • 04Assistant class with built-in tools and support for custom tools and streaming
  • 05RAG evaluation with RAGAS-style faithfulness and relevance scores

Use cases

  • Adding question answering over company documents to a Rails or Ruby app using RAG
  • Building a chat assistant that calls tools such as search or a database
  • Switching between LLM providers without rewriting application code
  • Evaluating the quality of a retrieval pipeline in Ruby

Quick start

  1. 1

    Add the gem to your Gemfile with Bundler

    bundle add langchainrb
  2. 2

    Or install the gem directly without Bundler

    gem install langchainrb
  3. 3

    Require the library in your Ruby code

Things to know

  • Additional gems may be required beyond the core gem, which is not included by default.
  • Most LLM and vector database integrations need provider API keys or separate services.

In collections

Open-source AI agent frameworks & apps

Topics

#llm#ruby#rag#vector-search#ai-agents#embeddings#agents#artificial-intelligence#machine-learning#ml

FAQ

What is langchainrb?
A Ruby library for building LLM-powered applications, offering a unified interface to many LLM providers, vector databases, RAG pipelines and assistants. Langchain.rb is a Ruby gem for building applications on top of large language models. It gives Ruby developers one interface to call providers such as OpenAI, Anthropic, Google Gemini, Mistral AI, Ollama and AWS Bedrock, so switching backends mostly means changing the class you instantiate.
Is langchainrb free to use? What license does it have?
langchainrb is open source under the MIT license. Check the license terms before using it in commercial products.
Is langchainrb still maintained?
Actively maintained. The last commit to langchainrb was on Oct 21, 2026.
What can I use langchainrb for?
Adding question answering over company documents to a Rails or Ruby app using RAG Building a chat assistant that calls tools such as search or a database Switching between LLM providers without rewriting application code Evaluating the quality of a retrieval pipeline in Ruby
How do I install langchainrb?
Add the gem to your Gemfile with Bundler: bundle add langchainrb Or install the gem directly without Bundler: gem install langchainrb Require the library in your Ruby code
Where can I get langchainrb?
The source code and installation instructions are on GitHub: https://github.com/patterns-ai-core/langchainrb

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