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How to Install DeepSeek Harness: A Step-by-Step Setup Guide for Developers

#deepseek #llm #opensource #aiagentharness

Building an AI coding assistant used to require stitching together dozens of libraries — until DeepSeek Harness changed the game. This open-source framework treats every capability as a plugin, from the model to the tools to the UI. In this guide, I’ll walk you through setting it up locally using Ollama (or OpenRouter) so you can have a private, powerful AI pair programmer running on your own machine in under 10 minutes.

Step-by-Step Guide to Set Up DeepSeek Harness

Step 1: Install/Update nvm (Node Version Manager)

This installs or updates nvm, which lets you manage multiple Node.js versions easily.

Command you ran:

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.40.1/install.sh | bash
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Step 2: Install Node.js v22 and Set It as Default

This downloads, installs, and switches to Node.js version 22.23.2, then sets it as the default for all future terminal sessions.

Commands you ran:

nvm install 22
nvm alias default 22
nvm use 22
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Step 3: Verify the Installation

This checks that Node.js and npm are now on the correct, compatible versions.

Commands you ran:

node -v # Output: v22.23.2
npm -v # Output: 10.9.8
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Step 4: Launch DeepSeek Harness

Now that your environment is properly set up, this is the command to start the actual Web UI:

bash

npx @deepseek-ai/dsh web
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Once it runs, open your browser to http://127.0.0.1:3080

Step 5: Activate OpenRouter (Pre-configured Provider)

OpenRouter is great because it gives you access to dozens of models (like Claude, GPT-4, DeepSeek, Llama) through a single API key, without needing a credit card for most free tiers.

5.1. Click on “OpenRouter” in the list

On your Settings > Models page, scroll down and click on the openrouter tile/row from the list of providers.

5.2. Enter your OpenRouter API Key

  • If you don’t have one, go to openrouter.ai/keys, sign up, and click “Create Key”. Copy it.
  • Paste that key into the API Key field that appears for the OpenRouter provider.

5.3. Pick a default model

  • In the settings for OpenRouter, you will see a “Models” or “Default Model” dropdown.
  • Select any model you like. For coding, popular choices are:
  • deepseek/deepseek-chat (Free/Cheap)
  • google/gemini-2.0-flash-exp:free (Free)
  • anthropic/claude-3.5-sonnet (Paid, but best for coding).

5.4. Click “Apply” or “Save”

  • Look at the bottom right of the settings panel and click the “Apply” button to save your changes.

5.5. Go back to the Chat and select OpenRouter

  • Click on the main Chat or New Session tab at the top.
  • In the model selector dropdown (usually at the top of the chat box), switch from “DeepSeek” to “OpenRouter” (or specifically the model you just selected, like deepseek/deepseek-chat).

Step 6: The Final Step — Send Your First Coding Prompt

This is the moment you’ve been waiting for. In the chat input box at the bottom (where you already typed “Hello!”), replace that with a real coding task and hit Send (Enter).

Here are 3 great first prompts tailored to your blog project. Pick the one that fits best:

Prompt Option 1 — Project Setup:

I want to build a modern blog website. Look at my current workspace folder and help me set up the best folder structure. Suggest whether I should use React, Next.js, or plain HTML/CSS.
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Prompt Option 2 — Write Actual Code:

Create a reusable React component called BlogCard. It should accept props for title, excerpt, author, and date. Style it with Tailwind CSS and make it responsive.
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Prompt Option 3 — Debug/Refactor:

Scan my current project files. Identify any outdated dependencies or code that could be improved, and suggest specific fixes.
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What Will Happen Next?

  • The agent will start working in real-time.
  • You will see it reading files, writing code, and running terminal commands.
  • If you open the Trajectory View (click the tab next to “Chat”), you can watch every single thought, tool call, and result — like having X-ray vision into the AI’s brain.

Conclusion: What Now?

You have transformed your computer into a powerful AI-driven development environment. DeepSeek Harness is now your personal AI coding assistant.

Here’s what makes this setup special:

  • Everything is traceable: If the AI makes a mistake, you can rewind, fork, and replay the exact session.
  • Modular: You can swap models, add tools, or create custom modes without touching the core code.
  • Real-world ready: It edits files, runs shell commands, searches the web, and can even manage subagents for complex tasks.

Thank you so much for reading

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