DeepSeek Harness developer preview DeepSeek Harness is now in developer preview for agent harness developers worldwide — source code included. Every capability is a plugin that can be swapped or recomposed: models, tools, skills, sessions, sandboxes, storage, loops, scheduling, and the UI. Harness keeps agents working in real-world environments The model is the soul of an agent. A harness lets an agent understand its environment, use tools, and keep working in real-world settings. The Cordis kernel manages plugin mounting, unmounting, and dependencies. Agent capabilities live in the plugins. Capabilities as plugins Plugins provide every agent capability, including models, tools, skills, sessions, sandboxes, storage, loops, scheduling, and the UI. Cordis services and events let the plugins work together. Compose with configuration Developers can select, swap, or extend any capability in configuration without changing the DeepSeek Harness source code. Everything is a plugin. Every run is traceable. Everything is a plugin DeepSeek Harness is built on Cordis 's plugin system. Plugins provide every agent capability, including models, tools, skills, sessions, sandboxes, storage, loops, scheduling, and the UI. Cordis services and events let the plugins work together. Developers can select, swap, or extend any capability in configuration without changing the DeepSeek Harness source code. Every run is traceable Everything the model sees is recorded in an append-only session log: system prompts, reasoning, tool calls and results, subagent scheduling, and every context injection. In the Trajectory view, you can inspect these records by source. Resume, fork, search, and replay all operate on the same event stream.

Multiple runtime modes Standard mode includes the full toolset. Code mode uses model-generated code to orchestrate multiple rounds of tool calls. Minimal mode keeps only a shell tool and a file editor for benchmarking models in a minimal environment. Creator mode lets you inspect the current runtime, test Cordis plugins in memory, and combine them into new modes. Everything is a plugin. Every run is traceable. Everything is a plugin DeepSeek Harness is built on Cordis 's plugin system. Plugins provide every agent capability, including models, tools, skills, sessions, sandboxes, storage, loops, scheduling, and the UI. Cordis services and events let the plugins work together. Developers can select, swap, or extend any capability in configuration without changing the DeepSeek Harness source code. Every run is traceable Everything the model sees is recorded in an append-only session log: system prompts, reasoning, tool calls and results, subagent scheduling, and every context injection. In the Trajectory view, you can inspect these records by source. Resume, fork, search, and replay all operate on the same event stream. Multiple runtime modes Standard mode includes the full toolset. Code mode uses model-generated code to orchestrate multiple rounds of tool calls. Minimal mode keeps only a shell tool and a file editor for benchmarking models in a minimal environment. Creator mode lets you inspect the current runtime, test Cordis plugins in memory, and combine them into new modes. Customize your DeepSeek Harness Try it now or install from source Install Node.js, then launch the Web UI with npx. Install from source Clone the full source and follow the setup instructions in the repository. Join the DSH plugin ecosystem DeepSeek Harness remains in developer preview and is still being tested by developers building agent harnesses. Its core plugins and APIs will continue to evolve. We look forward to exploring the limits of intelligence with developers worldwide using open-source infrastructure that is reusable and composable.