What Is an Agent Harness - The Everything-Is-a-Plugin Framework
In short, an agent harness is the framework that "makes agents run": it connects the model, provides the tools, manages sessions, sandboxes execution, and drives the loop. DeepSeek Harness turns all of that into replaceable plugins.
What is an agent harness
An agent harness is the underlying framework that runs and orchestrates AI agents. A complete harness typically handles:
- Model: connecting to and calling large models (such as deepseek v4)
- Tools: giving the agent callable tools (shell, file editing, search, and more)
- Sessions: keeping conversation history and context
- Sandbox: isolating the agent's execution environment
- Storage: persisting sessions and state
- Loops / scheduling: driving the "model → tool → model" back-and-forth
- UI: providing an interface
In one line: the harness decides what the agent can see, what it can do, and how it is driven.
What is harness engineering
Harness engineering is the practice of designing and building such frameworks: organizing model adaptation, tool registration, session logs, and loop scheduling into components that are maintainable, extensible, and replaceable.
Good harness engineering aims for:
- Composable: capabilities combine freely instead of being welded into one kernel
- Replaceable: swap a model or a sandbox without touching the rest
- Observable: every run leaves a trace
- Extensible: add capabilities without editing source code
DeepSeek Harness's answer: everything is a plugin
DeepSeek Harness (dsh) takes the core idea of harness engineering to its limit — everything is a plugin:
- Built on the Cordis plugin system, which offers spatiotemporal composability
- Model, tools, skills, sessions, sandbox, storage, loops, scheduling, and UI are all plugins
- Plugins cooperate through services and events, composed freely at the configuration layer
- There is no privileged kernel to patch
That is why dsh is both a usable agent harness and a framework you can freely reshape.
Why choose DeepSeek Harness
- 🧩 Everything is a plugin — swap one provider and you change the product
- 🔍 Every run is traceable — an append-only session log plus a Trajectory view
- 🧭 Four run modes — Standard / PTC (programmatic tool calling) / Minimal / Creative
- 🔓 MIT licensed — free to use, modify, and sell
FAQ
What is a harness?
"Harness" here means the framework that runs and orchestrates agents — model, tools, sessions, sandbox, loops, and scheduling. The explanation above is the full answer.
What is the difference between an ai harness and a coding agent?
An ai harness is a framework (build it yourself); a coding agent is an application (use it directly). See the comparison page.
I want to build my own agent — where do I start?
Start by installing DeepSeek Harness, then see the quick start.