DeepSeek Harness

DeepSeek Harness is DeepSeek's own agent runtime, the layer that sits between a model and your machine and gives it tools, memory, skills, and an interface. The architecture is one idea taken all the way: everything is a plugin. Models, tools, session storage, sandboxes, scheduling, even the agent loop itself are plugins composed into profiles, so you can swap almost any piece without forking the project. MIT licensed and free.

Running it is one command, npx @deepseek-ai/dsh web, which needs Node and serves a web UI on localhost port 3080. Building from source is a pnpm install and build. There is no server to operate: it runs on your machine and calls out to whichever provider you configure. A plugin ecosystem formed within days of launch, including native desktop wrappers and a terminal UI, all discoverable through the dsh-plugin topic on GitHub.

The harness costs nothing and the model calls are the only bill. DeepSeek's own API is cheap by frontier standards: V4-Pro is $1.32 per million input tokens and $3.96 per million output at peak, and exactly half that off-peak. Solo developers: free, and worth an evening if composable systems appeal to you. Small teams: free, but pin your version and mean it. Large teams: watch it rather than standardize on it.

The catch, and DeepSeek puts it in capital letters in their own README: this is a developer preview and there will be compatibility-breaking changes. The plugin API you build against this month may not exist next month. The popularity is real and so is the churn, so treat anything you write on top of it as disposable until the interfaces settle.