"Everything is a plugin" — model, tools, skills, sessions, sandbox, storage, loops, scheduling, and UI are all composed from plugins.

Overview What is dsh

DeepSeek Harness (dsh) is an open-source agent harness by DeepSeek AI, currently in developer preview (v0.1) and released under the MIT license.

Its purpose is clear: to provide an open, freely composable infrastructure for building and exploring agents. DeepSeek Harness follows an everything-is-a-plugin design — a plugin-based open architecture where model, tools, skills, sessions, sandbox, storage, loops, scheduling, and UI are all composed from plugins, freely swappable and recomposable.

As an early preview, many details are still being refined, and the core plugins and base interfaces will keep iterating quickly.

Design Design

Everything is a plugin

DeepSeek Harness is built on the Cordis plugin system, which offers spatiotemporal composability. The Cordis meta-framework handles only plugin loading, unloading, and dependencies; every concrete component of the harness is a distinct Cordis plugin. Plugins cooperate through Cordis services and events, and can be freely composed at the configuration layer.

Developers can select, replace, or extend any single capability as a plugin — without ever modifying DeepSeek Harness source code itself. That is the most important principle: everything is a plugin.

There is no privileged kernel to patch: you extend dsh by mounting plugins alongside other plugins, and every registration is a reversible side effect, undone when its plugin unloads.

Multiple run modes

DeepSeek Harness ships four modes, each loading a different plugin set:

Mode	Description
Standard	The complete tool set, out of the box
PTC	Programmatic Tool Calling — the model generates code that composes multiple rounds of tool calls
Minimal	Only a shell tool and a file-editing tool, for model benchmarking in a minimal environment
Creative	Inspect the current runtime, try Cordis plugins in memory, and compose new modes

Every run is traceable

Everything the model sees is written to an append-only session log — system prompts, chain-of-thought, tool calls and results, sub-agent dispatch, and every context injection.

In the Trajectory view you can inspect this information by source. Resume, fork, retrieval, and replay all share the same event stream.

Architecture Architecture

The architecture in one sentence: the product is a plugin tree, and every part is replaceable from configuration.

A running dsh = a plugin tree (layers stacked in order at startup)
        │
        ├─ profile (a named assembly): lists bundles, stores out-of-tree plugins, holds cordis.patch.yml
        ├─ bundle: the distribution format for Cordis config entries and their mount code
        └─ layers applied in order: profile bundles → profile patch → home patch → --patch overlay

Core packages (a few of those contributing to the Cordis tree):

Package	Responsibility
core/session	Append-only SessionEvent log and in-memory storage
core/system-prompt	Assembly of prompt sections and tool schemas
core/tools	Scoped tool registry with a gated execution pipeline
core/agent / core/agent-loop	The Agent interface and its default driver
llm/llm	Message and streaming vocabulary, plus the adapter seam

A seam is a replaceable capability with three roles: the Service Definition declaring the interface, the Service Provider implementing it, and the Consumer using it. Seams are why swapping one provider changes the whole product.

License License

DeepSeek Harness is MIT licensed — open source, free to use, modify, and sell. Source: github.com/deepseek-ai/deepseek-harness. Third-party licenses are listed in THIRD_PARTY_NOTICES.md.

Try it now Try it now

• Quick start: run npx @deepseek-ai/dsh web on a system with Node.js to launch the Web UI (default http://127.0.0.1:3080).
• From source: git clone https://github.com/deepseek-ai/deepseek-harness, then follow the repository instructions.
• See all options on the install page and the guide.
• Curious how it compares to Claude Code / Codex / OpenCode? See the comparison page.

In one sentence

DeepSeek Harness = everything is a plugin + Cordis composability + four run modes + traceable sessions — an open (MIT), reusable, composable agent harness.