Installation

Prerequisites

OpenSpec is a Node.js CLI. You need version 20.19.0 or newer.

In your terminal:

node --version

If that prints v20.19.0 or higher, you're set. If not, install a newer Node from nodejs.org or through your version manager (nvm, fnm, asdf, volta).

The workflow itself runs inside an AI coding tool: Claude Code, Cursor, or any other tool on the supported list.

Install with your AI assistant

Paste this into your AI chat:

Fetch https://raw.githubusercontent.com/Fission-AI/OpenSpec/main/install.md and follow it.

Or, in your terminal, pipe it into a CLI agent (Claude Code shown):

curl -fsSL https://raw.githubusercontent.com/Fission-AI/OpenSpec/main/install.md | claude

That fetches install.md at the repo root, a prompt written for any agent that can run shell commands (a few IDE integrations can't). Expect your assistant to:

1. Check your Node version, and stop if it's older than 20.19.0.
2. Skip the install if the CLI is already on your machine; otherwise show you the install command and wait for your confirmation before running it.
3. Verify openspec is on your PATH.
4. Name the folder it thinks you mean, suggest the AI tool you're already talking to, and ask which others you use, then run openspec init there (the project setup step).
5. Report what init created and the exact spelling to invoke OpenSpec in your tool.

It stops before anything privileged and never edits your shell startup files. The manual methods below are the source of truth; the prompt runs them for you.

This install method is new and can have varying results depending on model used. Only use if you're comfortable correcting AI mistakes - otherwise we reccomend following the standard method below.

Install methods

Install the CLI globally; setting up your project comes after.

In your terminal:

npm install -g @fission-ai/openspec@latest

Yarn

yarn global add is Yarn Classic (1.x) only. Modern Yarn removed global installs, so use npm, pnpm, or bun instead: a global CLI doesn't have to share your project's package manager.

Bun

Bun installs OpenSpec but doesn't run it: you still need Node on your machine (the prerequisite above). Without it, every command fails with env: node: No such file or directory. Bun treats every Node CLI this way.

Deno

Deno installs the CLI from npm and needs explicit permission flags. In your terminal:

deno install --global \
  --allow-read --allow-write --allow-env --allow-sys=cpus,homedir --allow-net=edge.openspec.dev \
  npm:@fission-ai/openspec@latest

Some commands launch another program: openspec config edit opens your editor. Deno interrupts those with a permission prompt on every run. To stop it asking, add a scoped --allow-run=<program> to the install command.

Nix

The OpenSpec repo ships a Nix flake. Install it into your profile; in your terminal:

nix profile install github:Fission-AI/OpenSpec

Or run a one-off command first, without installing:

nix run github:Fission-AI/OpenSpec -- --version

That leaves nothing on your PATH, so there's no install to check afterward.

To put OpenSpec in a project dev shell instead, add the flake as an input and use its default package; flake.nix lists the outputs.

Check it worked

Whichever method you used, in your terminal:

openspec --version

If that prints a version number, the CLI is on your PATH. It installs once per machine.

Next, set up your project; if your assistant already ran init, that page shows what it wrote and how to adjust it.

Updating

In your terminal, in each project where you ran init:

openspec update

When a newer CLI is out, openspec update says so and can install it for you; that upgrade is once per machine. Every run refreshes the project's generated skills and commands, which never update on their own. A current project prints ✓ All 2 tool(s) up to date (v1.7.0).

Uninstalling

To uninstall OpenSpec, run through the steps below; none of them touch your source code. You can also point your agent at this section and let it handle the removal.

1. Remove shell completions, if you set them up, while the CLI can still do it. In your terminal:

openspec completion uninstall

2. Remove the package. In your terminal:

npm uninstall -g @fission-ai/openspec

On Deno: deno uninstall --global openspec. On Nix: nix profile remove openspec. Your shell should no longer find openspec.

3. Delete what's left, or keep it.

• Generated agent files: openspec-* skills and opsx commands under directories like .claude/ or .agents/, per project. Supported tools lists each tool's paths; MiniMax Code keeps skills in ~/.minimax/skills.
• Leftovers from older versions: marker blocks in CLAUDE.md or AGENTS.md (delete the block, keep the file) and opsx-*.md prompts in ~/.codex/prompts.
• The openspec/ folder: pause first. specs/ and changes/archive/ are your record of the system, plain Markdown that reads fine without OpenSpec.
• Per-machine state: settings and the telemetry id in ~/.config/openspec/; schema overrides and store registrations in ~/.local/share/openspec/ (Windows: %APPDATA%\openspec, %LOCALAPPDATA%\openspec). Registrations are pointers; the store repos they point to are untouched.