What DeepSeek Harness is

It is not a new model and not an API client. It is DeepSeek's open-source agent runtime: it wires a model to the filesystem, terminal, web, skills, and other agents, and it records what the model did. MIT-licensed developer preview, released 2026-08-13. The repo is explicit: breaking changes will land.

Start it with:

npx @deepseek-ai/dsh web

The Web UI listens on http://127.0.0.1:3080 by default. Source installs use pnpm. Official site: deepseek.com/harness.

Everything is a plugin

The kernel is Cordis. A running harness is a Context. Packages register services, events, and reversible effects. The model adapter, tool table, session log, agent loop, and Web UI are plugins, and configuration can replace any of them. There is no privileged core to patch. You mount a community plugin beside the rest.

The smallest plugin exports `apply(ctx)`. `cordis.yml` lists module specifiers. A failed apply is loud. It is not skipped.

Profiles and bundles

A boot is a stacked plugin tree. A profile is a named composition in the Harness home. It lists bundles and keeps your `cordis.patch.yml`. Official templates are `web` and `headless`.

A bundle is a distributable set of Cordis config rows plus the code they mount. The `dsh` field in `package.json` is the identity: `dsh.profile` lists bundles, `dsh.bundle` points at a patch file. `dsh.client` can inject Web GUI code.

Stack order: bundles in the profile, then the profile patch, then the home patch, then `--patch`. A patch replaces a whole config row by id. It does not deep-merge. Write one new field and existing keys and URLs can disappear with the rest of the row.

How community plugins get found

Official does not take outside PRs. CONTRIBUTING is clear: put the GitHub topic dsh-plugin on the repo so people can search. Beta also used the dsh-external/hub catalog. This site turns those repos into a searchable market with copyable install commands.