---
title: "DeepSeek Harness"
description: "DeepSeek's open-source agent runtime built on the Agent = Model + Harness thesis: modular, traceable execution without hardcoded core logic."
section: "concepts"
type: "concept"
created: "2026-08-24"
updated: "2026-08-24"
confidence: "high"
tags: ["agents", "context-engineering", "subagents", "workflow", "evaluation"]
canonical: "https://pyweb.dev/wiki/deepseek-harness"
---
# DeepSeek Harness

**DeepSeek Harness** is an open-source agent runtime framework released by [DeepSeek](/wiki/deepseek) built around the architectural thesis `Agent = Model + Harness`. It provides a modular, traceable execution harness designed to keep autonomous agents functioning reliably in real-world environments without hardcoded core logic.

## Core Architectural Design

The system is designed around two primary engineering principles: **Everything is a plugin** and **Every run is traceable**.

### 1. The Microkernel & Capabilities as Plugins
DeepSeek Harness builds upon the [Cordis kernel](/wiki/cordis-framework), delegating all functional capabilities into plugins that register typed services:
- **Core Subsystems as Plugins:** Models (`ctx.llm`), tool execution (`ctx.tools`), sessions (`ctx.sessions`), agent swarms (`ctx.agents`), skills, sandboxes, storage, loops, scheduling, and UI are all decoupled plugins.
- **Dynamic Reconfiguration:** Developers can swap, compose, or extend capabilities purely through configuration without modifying the harness source code.

### 2. Append-Only Traceability & Trajectory Replay
Every interaction the model observes is captured in an append-only event stream:
- System prompts, reasoning thoughts, tool calls, tool results, subagent schedules, and context injections are recorded.
- In the **Trajectory View**, developers inspect runs by source.
- The primitives `resume`, `fork`, `search`, and `replay` all operate natively on the unified session event log.

## Multiple Runtime Modes

DeepSeek Harness includes 4 preset operational modes tailored for different development and benchmarking workflows:

1. **Standard Mode:** Full coding agent equipped with file editing, shell execution, search, skills, planning, goals, subagents, and workflows.
2. **Code Mode:** Exposes tools via the Code Mode SDK, enabling the model to write TypeScript programs that orchestrate complex, multi-step tool calls in a single execution step.
3. **Minimal Mode:** Constrained two-tool coding agent (`bash` and `str_replace_editor`) designed for clean model benchmarking.
4. **Creator Mode:** Metaprogramming environment designed for inspecting active runtimes, testing in-memory [Cordis](/wiki/cordis-framework) plugins, and authoring custom agent presets.

## Related Concepts
- [cordis framework](/wiki/cordis-framework)
- [agent harness engineering](/wiki/agent-harness-engineering)
- [agent native infrastructure](/wiki/agent-native-infrastructure)
- [subagents and context management](/wiki/subagents-and-context-management)
- [context engineering](/wiki/context-engineering)
- [deepseek](/wiki/deepseek)

---

## Agent Navigation

cluster: person (170 pages) | betweenness: 73.9

### References (outbound)
- [DeepSeek](https://pyweb.dev/wiki/deepseek.md)
- [Cordis Framework](https://pyweb.dev/wiki/cordis-framework.md)
- [Agent Harness Engineering](https://pyweb.dev/wiki/agent-harness-engineering.md)
- [Agent-Native Infrastructure](https://pyweb.dev/wiki/agent-native-infrastructure.md)
- [Subagents and Context Management](https://pyweb.dev/wiki/subagents-and-context-management.md)
- [Context Engineering](https://pyweb.dev/wiki/context-engineering.md)

### Referenced by (inbound)
- [Agent Harness Engineering](https://pyweb.dev/wiki/agent-harness-engineering.md)
- [Clean Architecture](https://pyweb.dev/wiki/clean-architecture.md)
- [Codex Harness Architecture](https://pyweb.dev/wiki/codex-harness-architecture.md)
- [Cordis Framework](https://pyweb.dev/wiki/cordis-framework.md)
- [DeepSeek](https://pyweb.dev/wiki/deepseek.md)

### Evidence (verified primary sources)
- [deepseek-harness-preview-2026](https://pyweb.dev/wiki/raw/articles/deepseek-harness-preview-2026.md) | origin: https://deepseek.com/harness/en/ | ingested: 2026-08-24 | sha256: d4c5c87f4ed70dd2bed5051988a96c07050c9dbcefa519e034c72da971a9747c
- [deepseek-harness-cordis-primer-2026](https://pyweb.dev/wiki/raw/articles/deepseek-harness-cordis-primer-2026.md) | origin: https://deepseek-harness.github.io/deepseek-harness/reference/cordis-primer | ingested: 2026-08-24 | sha256: e76a43328989f6f8a87a4299f0cbcf80120d985097a95863eba7cec2cf74fc1c

### Machine endpoints
- Knowledge graph: https://pyweb.dev/api/graph.json
- Graph analysis: https://pyweb.dev/api/graph-analysis.json
- Context index: https://pyweb.dev/llms.txt