Reasonix: an open-source DeepSeek coding agent you can leave running

Reasonix is an open-source coding agent built around DeepSeek models and shipped as a single Go binary under the MIT licence. Its authors describe it as one local engine with four ways in: a terminal interface, a desktop app, a browser-based web UI and an editor integration over ACP. Users supply their own DeepSeek API key, and the engine runs locally, so code is sent only to the model that has been configured.

Autonomy with an audit trail

The design centres on making long autonomous runs reviewable. Reads, writes and shell commands each request permission separately, and a workspace sandbox bounds what a command can touch even after approval. Plan mode holds every write until the plan has been read and approved. Each turn writes a checkpoint outside git, so a six-hour session can be rewound to any point without touching commit history.

Four surfaces, one engine

The CLI and full-screen TUI install with a single npm command and support macOS, Linux, Windows and WSL. The desktop app shows sessions side by side with settings, approvals and auto-updates. A local web UI starts with reasonix serve and, as the documentation notes, should get token or password authentication before it is exposed through a tunnel or remote port. Editors connect through reasonix acp, with an extension for VS Code and VSCodium and support for anything else that speaks ACP. Sessions, permissions, skills and MCP servers are shared across all four surfaces, and the codebase is mapped once per session.

Extending it, and what a session costs

External tools are merged into one registry through MCP over stdio, SSE and streamable HTTP, while markdown skills and subagents — explore, research, review and security-review — run with isolated tool sets. The project's example session shows the cost profile: on deepseek-v4-flash a task planned as three steps across two files with one test run finished with nine tool calls in 18 minutes for $0.043, at checkpoint 14. Reasonix is developed in public and lists 98 contributors; versions 1.38.3 and earlier need a full package install rather than the in-app updater to cross a change in the Electron shell.