DeepSeek Harness Desktop for macOS and Windows

What it claims

DeepSeek Harness is a preview agent harness in which tools, skills and UI surfaces are all plugins, built on Cordis. The page goes beyond the catalog summary by showing concrete mechanics. It shows the scheduled-task tool's argument shape, how Creator mode builds plugins from a bundled skill file, and what context the agent receives each turn. It also shows the controls in the composer.

How it works

• Plugins extend three things. They can add tools, skills and interface elements. The Creator-mode demo shows a plugin request ("Write a Pomodoro timer plugin") being handled like this: 1. The agent loads a skill named cordis-plugin-development. 2. It reads skills/cordis-plugin-development/SKILL.md. 3. It targets shell.overlay, which the page describes as "a frame-wide floating layer", for an always-on-top window.

So plugin authoring is guided by skill documents, and the UI exposes named mount points such as shell.overlay.

• Scheduled work is an optional plugin. The page says you must enable a "Scheduled tasks" plugin. Once enabled, a natural-language request becomes a schedule_create tool call with this shape:

{"prompt": "Summarize this week's project notes in a weekly report.",
 "title": "Weekly project report",
 "weekly": {"time": "17:00:00", "time_zone": "Asia/Shanghai", "weekdays": [5]}}

Time zones are IANA names, and weekdays are integers where 5 = Friday.

• Per-turn context. Each turn the model receives:
• a system prompt
• the user message
• a CONTEXT block holding the "workspace policy, available skills, and this turn's environment snapshot"
• Composer controls. The input box shows:
• a permission mode labeled "Workspace Write"
• a model selector set to "DeepSeek-V41-Flash" with a "High" setting, probably reasoning effort, though the page doesn't say
• / commands and @ references to files or earlier sessions
• Review and preview. Each turn produces a reviewable diff, for example src/label.ts +2 −1. Outputs can be previewed inline for .docx, .xlsx, .html, .ts, .py, .pdf and .md files.
• Developer tools. The trace view reports Duration, Turns, Calls and Search, and splits each step into Input, Model and Tools.

How to use it

The page names two run modes, the desktop app for macOS/Windows and "launch the web UI from code". It gives no install command, repository link or package name, so you will need to find those elsewhere.

Limits

• The page labels the release a preview with "evolving core plugins and APIs". Treat schedule_create and plugin mount points like shell.overlay as unstable.
• The page claims it is open source but names no licence.
• It gives no benchmarks, latency or cost figures, and no model sizes.
• It shows only DeepSeek-V4.1-Flash and does not say whether other models or providers can be plugged in.
• Permission modes other than "Workspace Write" are not described. Check sandboxing before you let it run scheduled or background scripts.