DeepSeek Harness web UI will not start

If npx @deepseek-ai/dsh web exits, hangs, or starts without opening a page, work through this checklist in order. Keep the original terminal output—the first error is usually more useful than later symptoms.

Confirm the command

Run the official package name exactly:

npx @deepseek-ai/dsh web

Do not substitute a similarly named community package. On the first run, npx may ask permission to download the package.

Check Node.js and npm

node --version
npm --version

If either command is missing, install a current Node.js LTS release. If Node is old, upgrade it, open a new terminal, and run the version checks again before retrying Harness.

Separate download errors from launch errors

Messages about package resolution, registries, DNS, certificates, or proxies occur before Harness starts. Check your npm registry and network policy. Corporate TLS interception can also prevent npm from downloading packages; use the configuration approved by your organization rather than disabling certificate verification.

If the package downloads and the terminal prints a local address, the launcher has probably succeeded.

Open the printed local address

The current preview commonly uses http://127.0.0.1:3080, but the terminal output is authoritative. Copy that address into the same machine’s browser. 127.0.0.1 is local to the machine running the process; it will not automatically work from another device.

Check for a port conflict

An “address already in use” or EADDRINUSE error means another process owns the requested port. Stop the earlier Harness process or identify the local process that is using the port. Avoid terminating an unknown process until you know what it is.

Keep the terminal alive

Closing the terminal or pressing Ctrl+C stops the local server. If the page worked and then disappeared, start the command again and leave the process running.

When to report an upstream issue

If the failure still occurs on a current Node.js release with the exact command, collect the operating system, Node version, command, complete error output, and minimal reproduction steps. Remove keys, paths, and repository content before posting to the official issue tracker.