DeepSeek Harness is an open‑source desktop application for macOS and Windows that implements Cordis’s “everything is a plugin” architecture, allowing users to run it as a native app or launch its web UI from code. The harness provides a unified workspace for everyday tasks such as organizing files, analyzing spreadsheets, drafting documents, and creating slides; coding activities like exploring repositories, fixing bugs, building features, and executing tests; research workflows for finding information, verifying facts, and citing sources; and background operations including script execution, batch file processing, and progress tracking. Functionality is extended through plugins that can be installed or created in “Creator mode” via chat, where users write plugin code, define metadata in package.json, implement client‑side logic, and install the bundle through the plugin manager. An example demonstrates building a floating Pomodoro timer plugin: reading the Cordis plugin development skill, configuring an overlay, inspecting providers, writing package.json and client.js, installing the bundle, and verifying the live plugin state, which took 5 minutes 24 seconds. Additionally, the Scheduled tasks plugin enables recurring jobs, illustrated by a weekly report generated every Friday at 17:00 Beijing time. Users can preview outputs directly in the workspace and refine them through conversational feedback, with access to developer tools for inspecting execution traces and runtime details to troubleshoot tool calls and task execution.