Installation

Prerequisites

• Node.js 20.19.0 or higher — Check your version: node --version

Package Managers

npm

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

pnpm

pnpm add -g @fission-ai/openspec@latest

yarn

yarn global add @fission-ai/openspec@latest

bun

Bun can install OpenSpec globally, but OpenSpec currently runs on Node.js. You still need Node.js 20.19.0 or higher available on PATH.

bun add -g @fission-ai/openspec@latest

Nix

Run OpenSpec directly without installation:

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

Or install to your profile:

nix profile install github:Fission-AI/OpenSpec

Or add to your development environment in flake.nix:

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    openspec.url = "github:Fission-AI/OpenSpec";
  };

  outputs = { nixpkgs, openspec, ... }: {
    devShells.x86_64-linux.default = nixpkgs.legacyPackages.x86_64-linux.mkShell {
      buildInputs = [ openspec.packages.x86_64-linux.default ];
    };
  };
}

Verify Installation

openspec --version

Updating

Upgrade the package, then refresh each project's generated files:

npm install -g @fission-ai/openspec@latest   # or pnpm/yarn/bun equivalent
openspec update                              # run inside each project

openspec update regenerates the skill and command files for the tools you've configured, so your slash commands stay current with the installed version.

Uninstalling

There's no openspec uninstall command, because OpenSpec is just a global package plus some files in your project. Removing it is a few manual steps, and nothing here touches your source code.

1. Remove the global package:

npm uninstall -g @fission-ai/openspec   # or: pnpm rm -g / yarn global remove / bun rm -g

2. Remove OpenSpec from a project (optional). Delete the openspec/ directory if you no longer want its specs and changes:

rm -rf openspec/

Think before you do this: openspec/specs/ and openspec/changes/archive/ are your record of how the system behaves and why it changed. If you might want that history, keep the folder (or keep it in git) even after uninstalling.

3. Remove generated AI tool files (optional). OpenSpec writes skill and command files into per-tool directories like .claude/skills/openspec-*/, .cursor/commands/opsx-*, and so on. Delete the openspec-* skills and opsx-* commands for whichever tools you configured. The exact paths per tool are listed in Supported Tools.

If you also have OpenSpec marker blocks in files like CLAUDE.md or AGENTS.md, remove those blocks by hand; your own content in those files is yours to keep.

Next Steps

After installing, initialize OpenSpec in your project:

cd your-project
openspec init

See Getting Started for a full walkthrough.