DeepSeek Harness Released: "Everything is a Plugin" & Cordis Architecture Breakdown

DeepSeek Harness is DeepSeek's production-grade AI agent execution infrastructure.

Official Website: https://deepseek.com/harness/
GitHub Repository: https://github.com/deepseek-ai/deepseek-harness

Core Philosophy: Agent = Model + Harness#

DeepSeek introduced the foundational engineering formula:

$$\text{Agent} = \text{Model} + \text{Harness}$$

• Model: The soul of the Agent, providing base reasoning and understanding.
• Harness: Grants the Agent the ability to understand environments, use tools, and work continuously in real-world scenarios.

Core Architecture: "Everything is a Plugin"#

DeepSeek Harness is built on the Cordis plugin framework:

• Cordis Kernel: Handles only plugin loading, unloading, and dependency management.
• Capabilities Provided by Plugins: Models, tools, skills, sessions, sandboxes, storage, loops, scheduling, and UI are all provided by plugins and collaborate via Cordis services and events.
• Compose in Configuration: Select, replace, or extend capabilities in configuration without modifying DeepSeek Harness source code.

graph TD
    subgraph CordisKernel["Cordis Kernel (Plugin & Dependency Manager)"]
        Kernel[Cordis Core]
    end

    subgraph Plugins["Capabilities Provided by Plugins"]
        ModelPlugin[Model Plugin]
        ToolPlugin[Tool & Skill Plugins]
        SessionPlugin[Session & Log Plugins]
        SandboxPlugin[Sandbox Plugin]
        UIPlugin[UI & Scheduler Plugins]
    end

    CordisKernel ---> Plugins
    Plugins ===> Agent[DeepSeek Harness Agent]

Traceable Runs (Trajectory Tracking)#

Everything seen by the model is logged in an append-only session log, recording system prompts, thought chains, tool calls & results, sub-agent dispatches, and context injections.

In Trajectory view, inspection by source, restoration, forking, searching, and replaying share the exact same event stream, guaranteeing full transparency.

Four Agent Preset Modes#

1. Standard Mode: Full-featured coding agent with file editing, Shell, search, Skills, plans, and workflows.
2. PTC Mode (Programmatic Tool Calling Mode): Exposes tools via Code Mode SDK, allowing models to combine tool steps using TypeScript programs.
3. Minimal Mode: Dual-tool agent (bash + str_replace_editor) designed for minimal model benchmark testing.
4. Creative Mode: Experiment with Cordis plugins in memory to compose custom presets.

Quickstart & License#

• Launch Web UI: npx @deepseek-ai/dsh web
• Source Clone: git clone https://github.com/deepseek-ai/deepseek-harness
• Developer Docs: https://deepseek-harness.github.io/deepseek-harness/guide/quickstart
• License: MIT License, © 2026 Hangzhou DeepSeek AI Co., Ltd.