Written by Jakub Rusinowski · Published August 17, 2026
DeepSeek Harness (dsh) is DeepSeek's new open-source, plugin-based agent harness. Here's how to install it — npx quickstart, full source build, web UI and headless configuration, and your first cordis.yml plugin — plus what to watch out for while it's still a developer preview.
An "agent harness" is the scaffolding around a model that turns it from a chat window into something that can read a repository, run shell commands, edit files, and carry a multi-step task to completion — the system prompt assembly, the tool registry, the loop that decides "call another tool or stop and answer," and the sandboxing around all of it. DeepSeek Harness is DeepSeek's entry in that category, and its defining choice is architectural: everything is a plugin. It's built on Cordis, a small plugin runtime whose design is documented as "a programming paradigm for spatiotemporal composabil…