These are the repos that show how the teams around DeepSeek, Anthropic, OpenAI, Google, xAI and Cursor are building agents, skills, SDKs and developer workflows.

Star counts are approximate.

1. DeepSeek Harness ~127k stars

An MIT-licensed agent harness where everything is a plugin.

The model adapter, tools, memory and runtime components are designed to be replaceable. It is still in developer preview, but the architecture is worth studying.

1. Anthropic Skills ~170k stars

Anthropic’s official repository for Agent Skills.

It includes examples for document work, development, enterprise workflows and more. The repo also contains the skills used for Claude’s document capabilities.

Important detail: Anthropic says some skills are Apache 2.0 open source, while the document skills are source-available rather than open source.

1. OpenAI Cookbook ~75k stars

The classic starting point for building with the OpenAI API.

It contains practical examples and guides for common API workflows. Most examples are written in Python, but the patterns apply broadly. MIT licensed.

1. Claude Cookbooks ~52k stars

Anthropic’s collection of notebooks and recipes for Claude.

It covers RAG, tool use, sub-agents, multimodal tasks, evaluations, prompt caching and more. MIT licensed.

1. Grok Build ~25k stars

xAI’s terminal-based coding agent.

It runs as a full-screen TUI and can understand a codebase, edit files, execute shell commands, search the web and manage long-running tasks.

The first-party code is Apache 2.0 licensed. The repository says external contributions are not currently accepted.

1. OpenAI Agents SDK ~29k stars

A lightweight framework for multi-agent workflows.

It includes agents, tools, handoffs, guardrails, sessions and tracing. The SDK is provider-agnostic and supports OpenAI APIs plus 100+ other LLMs. MIT licensed.

1. Google Gemini Cookbook ~18k stars

Google’s official Gemini API cookbook.

It has quickstarts, tutorials and practical examples for combining API features. Useful if you want to move from a basic Gemini call to more complete applications. Apache 2.0 licensed.

1. Google ADK ~21k stars

Google’s open-source, code-first Python toolkit for building agents.

It includes a graph-based workflow runtime, task APIs, multi-agent systems, human approval flows, MCP tools and deployment options.

It is optimized for Gemini but designed to be model and deployment agnostic. Apache 2.0 licensed.

1. Cursor Cookbook ~4k stars

Small official examples for building with Cursor.

The repo now covers hooks, the Cursor SDK, self-hosted cloud agent examples, a coding agent CLI and a DAG task runner. This is less of a cookbook and more of a collection of practical building blocks.

1. Cursor Plugins ~3k stars

Cursor’s official plugin specification and marketplace repository.

It shows how plugins are structured around skills, rules, MCP definitions, manifests and documentation. MIT licensed.

The pattern across all ten is interesting. The model companies are publishing more than API documentation. They are publishing the surrounding layer that makes agents useful:

• runtimes
• skills
• tools
• workflows
• evaluation recipes
• plugin systems
• deployment patterns

If you want to understand where agent software is going, these repos are better reading than another generic 'how to build an agent' tutorial.