How to Use DeepSeek Harness: The MIT-Licensed Open-Source Agent Foundation

What DeepSeek Harness is

DeepSeek Harness is an open-source agent foundation released by DeepSeek AI.

The everything-is-a-plugin design

Its character comes down to a single idea: everything is a plugin. The project released v0.1 as a developer preview on August 13, 2026, stating that models, tools, skills, sessions, sandboxes, filesystems, loops, orchestration, and the UI are all implemented as plugins. Replacing or extending any of them is a matter of recomposition rather than modifying the core.

No privileged core to patch

Looking a little deeper makes the design philosophy clearer. The official documentation says there is no privileged core to patch, and that you add functionality by mounting a plugin beside the others. The model adapter, the tool registry, the session log, and the agent loop itself are all plugins, replaceable from configuration.

How to use DeepSeek Harness

Two launch paths are provided. If you only want to try it, the npm route is faster.

The shortest path with npx

As long as Node.js is installed, the following single line brings up the Web UI. The default address is http://127.0.0.1:3080.

npx @deepseek-ai/dsh web

The Node.js version requirement is ^22.19.0 || >=24.0.0. It will not start on an older Node, so checking that first saves you a detour.

Running from source

If you want to work on the internals, fetch the repository. The package manager is pnpm: clone, install, build, then start.

git clone https://github.com/deepseek-ai/deepseek-harness.git
cd deepseek-harness
pnpm install
pnpm run build
pnpm dsh web

How it is composed, and what to watch for

Two units make that replaceability work: profiles and bundles.

Profiles and bundles

What gets assembled at boot is a layered plugin tree. A profile is a named composition that lists the bundles it stacks, and web and headless ship as templates. A bundle is a distribution format for config rows and the code they mount, and it stays patchable by the layers above it. You can check what is actually running in your environment with the following command.

dsh --profile web --dump-config

What to keep in mind

A design that is free to swap is, flipped around, one whose behavior shifts substantially with configuration. Given that compatibility-breaking changes will land during the preview, trying it in an isolated environment is more realistic than wiring it into daily production tooling. For the model side, see the DeepSeek model articles.

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