DeepSeek Harness vs Codex vs Claude Code

The short version

Runtime and interface shape

• DeepSeek Harness boots a named profile as ordered Cordis bundles and plugins. Its official web and headless profiles share a replaceable runtime, and the durable session event log drives history, replay, and UI state.
• Codex CLI opens a coding loop inside a repository. It can inspect files, edit them, run installed tools, accept steering during a turn, and run non-interactively through codex exec. Codex is also available through IDE, desktop, web, and cloud surfaces.
• Claude Code begins from the coding workflow rather than a general plugin tree. Its official surfaces include terminal, IDE, desktop, and browser, with project work spanning file edits, commands, Git, CI, and parallel agents.

Tools, permissions, and extensions

1. 01

   DeepSeek Harness: compose the runtime

   Tools execute through scoped registries, capability providers, sandbox and approval policy, and lifecycle events. Plugins can replace model adapters, tools, filesystem or subprocess backends, session behavior, and Web Client nodes. Profiles and bundles are the main distribution units.

2. 02

   Codex: configure the coding Agent

   Users choose the model, reasoning effort, permissions, and commands for a task. Repository instructions, skills, plugins, MCP, configuration, and non-interactive execution extend the working loop without requiring the user to rebuild the whole runtime.

3. 03

   Claude Code: customize the coding workflow

   Permission modes govern tool use. CLAUDE.md stores project instructions, Skills package repeatable workflows, Hooks run commands around actions, MCP connects external systems, and custom agents or Agent Teams divide work.

4. 04

   Keep the trust boundary visible

   All three can touch source files and run commands when authorized. Compare their active permission configuration, workspace boundary, installed extensions, and recovery path before allowing unattended work.

Choose by the job and ownership model

• Choose DeepSeek Harness when you want a runnable local Agent product and also need to own how its providers, tools, policies, sessions, and browser UI are composed.
• Choose Codex when the center of gravity is repository work, code review, scripting or CI, and a focused workflow that can span local and cloud surfaces.
• Choose Claude Code when its terminal-to-IDE coding workflow, CLAUDE.md convention, Skills, Hooks, MCP, and agent coordination match how your team already works.
• Run a small task in the real target environment before standardizing. Check permissions, diffs, command visibility, session recovery, and how clearly a teammate can understand what happened.