OpenSpec — Fluid Spec-Driven Development

"Fluid not rigid. Iterative not waterfall. Built for brownfield." Lighter alternative to Spec Kit — no phase gates, works on existing projects.

vs Spec Kit

Installation

npm install -g @fission-ai/openspec@latest
cd your-project
openspec init

# Opt out of telemetry
export OPENSPEC_TELEMETRY=0

Core 3-Command Workflow

1. /opsx:propose "feature name"  → generates change folder
2. /opsx:apply                   → AI implements tasks
3. /opsx:archive                 → moves to archive

Change Folder Structure

.openspec/changes/<feature-name>/
├── proposal.md     ← rationale and scope
├── specs/          ← requirements and scenarios
├── design.md       ← technical approach
└── tasks.md        ← implementation checklist

All Commands

CLI Commands

openspec init              # initialize in project
openspec config profile    # select workflow type
openspec update            # refresh agent instructions + slash commands

Key Principles

• No phase gates — update any artifact at any time
• Brownfield first — works on existing codebases
• Context management — clear context before implementation phases
• Best with Opus 4.5+ — high-reasoning models get best results
• 20+ AI tools — Claude Code, Cursor, Copilot, Windsurf, etc.