DeepSeek Harness Developer Preview: Everything is a Plugin

DeepSeek Harness is now available as a Developer Preview. It’s a framework for building AI agents. Everything is a plugin. Every capability – models, tools, UI – is an interchangeable plugin. This article explains the architecture, the Cordis core, and the runtime modes. We also cover how composable systems affect agent development, plus configuration files and trajectory logs.

Overview

DeepSeek Harness is in developer preview. It’s open source on GitHub. Developers can use the code to build or extend agents. The framework runs on the Cordis kernel, which handles mounting, unmounting, and plugin dependencies. Agents get capabilities only through plugins: models, tools, skills, sessions, sandboxes, storage, loops, scheduling, and UI. You can swap components via configuration without touching source code. Every model interaction is recorded in an append-only session log. The trajectory view makes that log inspectable.

Prompt Analysis

The article has no explicit prompts. This example demonstrates the configuration model. Developers define agents via configuration files or the Creator mode interface.

The Prompt

{
  "agent": "my-coding-agent",
  "mode": "standard",
  "plugins": {
    "model": "deepseek-chat",
    "tools": ["file-editor", "shell", "web-search"],
    "skills": ["python-development", "debugging"],
    "session": "append-only-log",
    "sandbox": "docker-isolated",
    "storage": "local"
  },
  "trajectory": {
    "record": true,
    "access": "resource-based"
  }
}

Components

The example shows the plugin structure. First comes the agent name, then the runtime mode – ‘standard’ includes all tools. Under ‘plugins’, capabilities are objects. The model is a DeepSeek chat model. Tools include file editor, shell, and web search. Skills are special instructions or workflows. Sessions are append-only logs, and sandbox runs isolated. Storage and trajectory recording complete the setup. Every component is interchangeable – that’s the core idea.

Frequently Asked Questions

What is the difference between Standard Mode and Code Mode?

Standard Mode has all tools: file editing, shell, file and web search, skills, planning, goals, sub-agents, and workflows. Code Mode adds the Code Mode SDK. That lets the model combine multiple tool calls in a single TypeScript program. Code Mode fits complex, multi-step tasks where the agent writes code to execute actions.

How does the Trajectory View work?

The Trajectory View shows everything the agent sees during a run: system prompts, reasoning steps, tool calls and results, sub-agent planning, and context injections. That data lives in an append-only session log – nothing gets deleted. Developers can filter by source, replay runs, fork, search, or re-inject them. This makes error tracking and optimization easier.

What operating modes are there?

DeepSeek Harness has four modes: Standard, Code, Minimal, and Creator. Standard includes the full toolset. Code adds the Code Mode SDK. Minimal has just two tools – a persistent bash shell and a file editor – for benchmark testing. Creator is for building new presets. It adds runtime inspection, plugin experiments, and instructions for your own presets.

How can developers create their own plugins?

Test plugins in Creator Mode. It loads Cordis plugins into memory, checks their functionality, and combines them via configuration. Save plugins as custom presets and reuse them across projects. The official docs and GitHub community show more examples and APIs.

Is DeepSeek Harness ready for production use?

DeepSeek Harness is still in Developer Preview. The framework works, but core plugins and APIs will change. It’s fine for experiments and prototypes, not for critical production. The MIT license allows free commercial use, subject to the Safe Use Policy.

What role does Cordis play?

Cordis manages plugins. It mounts and unmounts them, handles dependencies, and offers services and events for communication. That gives a loosely coupled architecture – you can exchange components without affecting others. This is the basis for the ‘Everything is a plugin’ principle.

Source

Based on this article.