DeepSeek Harness

DeepSeek Harness is an open-source coding agent created by DeepSeek: a program that runs on your machine and uses an AI model to read, write and modify code following your instructions. It was presented in 2026 as a developer preview, under the MIT licence (which lets you use and modify it freely), at the same time as the DeepSeek-V4-Pro model (checked in September 2026).

The word that tends to throw people is "harness": it's the program that surrounds the AI model and gives it hands, that is, access to files and tools and a working loop to carry out tasks step by step. What sets DeepSeek Harness apart is that everything in it is a swappable plugin: the model, the tools, the sessions, the interface… It can even use Claude Code or Codex as helpers, and it comes with a local web app as well as the command line (checked in September 2026). Being a preview, it can change quite a bit from one version to the next.

Since I work mainly with Claude and also use DeepSeek, this was a tool I had to try seriously. In "Ten days working with DeepSeek Harness" I explain what it was like bringing it into my real work, with its installation, its first tasks and the comparison with what I already use. If you're thinking of installing it, read that first: it'll save you a surprise or two, and remember that, since it's a preview, what I describe may change with the next updates.