Alternatives to Mellea

Python library for guaranteed valid structured outputs from LLMs using FSM constrained decoding

Guidance is an open-source Python library for constrained LLM generation with regex, CFG, and native control flow.

GoAI SDK: one unified Go API across 25+ LLM providers with streaming, structured output, MCP support.

Vercel AI SDK is an open-source TypeScript toolkit for building AI apps with 100+ models, real-time streaming, fallbacks, and agents

Free GitHub repo of OpenAI API code examples, guides, and Jupyter notebooks.

Run LLMs in-browser with WebGPU — headless React hooks, just useLLM().

Open-source Swift package wrapping the OpenAI API with async/await and Combine.

LMQL is a programming language for LLM interaction with typed constraints, nested queries, and multi-backend portability.

Extra-small OpenAI-compatible AI SDK for JS — 40x smaller installs.

The open-source Python library for loading, fine-tuning, and running transformer models across text, vision, audio, and video.

An open-source Python framework that turns ordinary functions into AI-powered tools via simple decorators.

Pydantic AI is the Python AI SDK for typed agents, realtime voice, image generation, and embeddings — every model a string swap away.

Type-safe Rust library for building AI agents across 20+ providers

Open-source streaming-first toolkit that turns AI agent output into interactive UI, not JSON.

Google's open-source framework for building agentic AI apps in JS, Go, Python & Dart.

A Rust library for building fast, streaming LLM pipelines — indexing, retrieval, and autonomous agents.

Open-source Python framework turning messy text into typed, queryable Semantic DataFrames

Fast Java tokenizer library for OpenAI GPT models using BPE

Open-source Python & TypeScript SDK for building production-grade AI agents with hooks, model routing, and cost controls.

EffGen is a Python framework for building AI agents on small language models, run locally or through any OpenAI-compatible server.

Open-source Java library for building LLM-powered apps with a unified API

Open-source Rust tokenization library for training BPE, WordPiece and Unigram vocabularies at production speed.

Open-source Rust CLI that filters command output before it hits your LLM

Mirascope: Build LLM apps with decorators, observability, and full control.

Enterprise-managed LLM fine-tuning and serving platform by Rubrik

The frontend stack for agentic user experience — drop-in chat, generative UI, and shared state for React apps on any AG-UI backend

Type-safe programming language for building AI agents with compile-time guarantees.

Open-source LLM that turns natural language into API calls for tool-using agents

Go-native LLM framework by ByteDance for building production-grade AI applications.

Open-source framework for building private, on-premise RAG applications with 100% local data control.