DeepSeek open sources an agent harness where everything is a plugin

DeepSeek on Thursday open sourced DeepSeek Harness, a Node.js agent runtime now sitting on GitHub as a developer preview under the MIT license. The early response was loud enough to notice: the repository picked up more than 33,000 stars within hours, and the count kept moving.

The hook is simple and a little severe. DeepSeek says “everything is a plugin,” and it means it. The model adapter, tool registry, session log, and even the agent loop can all be swapped out. There is, as the docs put it, “no privileged core to patch.” Instead, extending the system means mounting another plugin beside the rest.

That structure comes from Cordis, which the team describes as a “meta-framework for spatiotemporal composability.” Strip away the grand phrasing and the point is practical: modern agent systems need components that can be added, removed, and recombined without breaking the whole machine. A paper from three researchers at Peking University and DeepSeek lays out that idea and underpins both Cordis and the harness.

DeepSeek ships the harness with four presets. Standard mode gives developers the full coding agent setup, including filesystem tools, shell access, web search, subagents, and a plan mode. Minimal pares that down to bash and str_replace_editor. Code mode changes the shape of tool use entirely by generating a TypeScript SDK and having the model write against it, so a multi-step exchange can collapse into a single call. Creator mode is for building custom presets and adds runtime inspection, plugin experiments, and preset-authoring guidance.

Logging is another big constraint. Everything the model sees has to be reconstructable from an append-only session log, and that same event stream powers resume, fork, replay, transcripts, telemetry, and the web UI. DeepSeek also wraps local execution in sandboxing for Linux, macOS, and Windows, so the thing is built with the usual agent paranoia baked in.

The harness is not locked to DeepSeek’s own model family either. The provider list includes Anthropic, OpenAI, AWS Bedrock, Microsoft Azure, Google’s Gemini Enterprise Agent Platform, and DeepSeek’s own endpoint, plus custom OpenAI-compatible gateways. It also ships with subagent providers for Anthropic’s Claude Code and OpenAI’s Codex, both off by default, along with bridges for existing hooks.json files, MCP client support, Agent Client Protocol support, and the ability to read AGENTS.md and CLAUDE.md files.

DeepSeek is not taking outside pull requests right now, and points people toward GitHub Discussions and plugin work instead. That makes the repository less a normal open-source project than a staged demonstration of a design idea. In a field crowded with coding agents, that may be the point: open the architecture, not just the code.