DeepSeek Harness is an open-source agent harness developed by DeepSeek AI. It is built on an everything-is-a-plugin architecture and powered by Cordis, whose design is described in 'A Programming Paradigm for Spatiotemporal Composability'.

The platform features a composable plugin system that extends what agents can do. Users can install official plugins, create them through chat in 'Creator mode', or develop their own to fit specific workflows. The harness supports a wide range of tasks including organizing files, analyzing data, drafting documents, creating slides, coding activities like exploring repositories and fixing bugs, research tasks such as finding information and citing sources, and background tasks like running scripts and batch-processing files.

DeepSeek Harness plugin manager interface showing listed official plugins and an Add plugin action button
Plugin manager with official plugins and Add plugin actionwww.deepseek.com

The article describes a composable plugin system where users install official plugins, create them via chat, or build their own; this screenshot illustrates that ecosystem at a glance.

DeepSeek Harness can be used as a desktop application or launched as a web interface from code. To get started, users install Node.js and run the Web UI with npx @deepseek-ai/dsh web, which starts the server at http://127.0.0.1:3080 by default. For source installation, users clone the repository, install dependencies with pnpm, build the artifacts, and run the harness.

The plugin ecosystem includes official plugins, agent team plugins, and experimental plugins covering areas like auto-approval review, scheduled tasks, voice input, terminal integration, agent loops, and subagents. Examples demonstrated in the documentation show how to create a Pomodoro timer plugin and set up scheduled tasks for weekly project reports that run every Friday at 17:00 Beijing time.

DeepSeek Harness trajectory view displaying a timeline of tool calls and execution details
Trajectory view with timeline, tool calls, and execution detailswww.deepseek.com

The article discusses agent loops, subagents, and background execution; this trace view shows how the harness records and displays tool calls and step-by-step agent behavior.

DeepSeek Harness is currently in public preview worldwide, with the company noting that it is in developer preview and iterating rapidly, indicating there may be compatibility-breaking changes as the platform evolves.