Alternatives to Mellea

Marvin is an open-source Python framework that turns LLM calls into typed functions, agents, and Pydantic-validated results.

Pydantic AI is the typed, open-source Python agent framework that returns Pydantic-validated objects from every run.

Mirascope is an open-source Python library that turns LLM calls, tools, and prompt versioning into plain decorated functions.

Python library for constrained LLM generation with regex, context-free grammars, and inline control flow.

Outlines is a Python library for structured generation that constrains LLM decoding so JSON, regex, and grammar outputs are valid every

Open-source TypeScript SDK for streaming AI apps and agents across 100+ models, with built-in provider fallbacks

Unified C# .NET library for calling 15+ LLM providers through a single strongly-typed API.

Free OpenAI API examples and Python notebooks for building chat, embeddings, and RAG apps

LMQL is a programming language for LLMs that uses types, templates and constraints to make prompts modular and outputs reliable.

Go SDK for AI apps: one type-safe API for text generation, streaming, tools and MCP across 25+ LLM providers.

xsAI is an extra-small OpenAI-compatible AI SDK for JavaScript and TypeScript, 13.0 KB gzipped with every package included.

BAML is a type-safe, Turing-complete language for agentic and LLM code that compiles typed Python and TypeScript SDKs.

TypeLLM returns typed, schema-conformant values from text and images in one API call — no JSON repair loops.

Genkit is Google's open-source AI SDK for building agentic AI apps in TypeScript, Go, Python, and Dart.

DiscuroAI chains GPT-3 prompt templates and DALL-E 2 image calls into multi-step workflows you run with one API request that returns JSON.

Open-source LLM from UC Berkeley that turns natural language into API calls and tool-using agent actions.

A Scala library that calls OpenAI's HTTP APIs from the JVM with typed, effect-friendly code

SwiftOpenAI: an MIT-licensed Swift package for calling the OpenAI API with native async/await and Combine on Apple platforms.

OpenUI turns AI agent responses into streaming generative UI built from your own component library.

Hugging Face Tokenizers: train BPE, WordPiece and Unigram vocabularies and tokenize a GB of text in under 20 seconds.

PrivateGPT is the open-source on-premise RAG framework for local document Q&A — 57k GitHub stars, zero cloud calls.

Open-source Ruby gem that calls 11 LLM providers through one consistent interface for embeddings, completions, and chat.

Fabric turns reusable AI prompt patterns into chainable command-line workflows you can inspect and run in your terminal.

Rig is an open-source Rust LLM framework for shipping type-safe AI agents across 20+ providers.

Native PHP SDK for LLM inference, typed object extraction, agents, and coding-agent control.

TOON is an open-source, token-efficient encoding of the JSON data model for LLM prompts, using 42.6% fewer tokens than JSON.

A type-safe, open-source TypeScript library for orchestrating multi-step AI workflows on top of the Vercel AI SDK.

Open-source Java library that tokenizes text with OpenAI's BPE encodings so you can count, encode and decode locally

Local MCP context gateway that compresses and filters what your AI coding agent reads

Open-source framework for adding agent chat, generative UI, and human approvals to React apps on any agent backend.