OpenSpec is an open-source spec-driven development (SDD) framework by Fission-AI that formalizes how developers collaborate with AI coding assistants. Instead of ad-hoc prompting that leaves intent ambiguous, OpenSpec adds a lightweight spec layer so you and your AI agents agree on what is being built before any code is written. The framework organizes every change in dedicated folders for proposals, specs, design notes, and tasks — turning AI-assisted development from a series of one-off conversations into a reviewable, version-controlled workflow.
The key concept that makes OpenSpec practical for real codebases is the delta spec: rather than restating an entire system specification for each change, delta specs describe only what is changing. This approach makes OpenSpec a natural fit for brownfield development where most work involves extending or refactoring existing systems rather than greenfield builds. Workflows are deliberately fluid with no rigid phase gates, so developers can create artifacts in any order that matches how they actually think about a problem. The propose workflow generates a complete change proposal — design, specs, and tasks — from a single request.
OpenSpec is distributed as a CLI tool that integrates with 21+ AI coding assistants out of the box, including Claude Code, Cursor, Windsurf, Continue, Gemini CLI, GitHub Copilot, Amazon Q Developer, Cline, Aider, and more. Running openspec init configures the selected tool using your active profile and chosen workflow, so each AI assistant reads specs in a consistent format. The project is developed in the open on GitHub under the Fission-AI organization and is freely available for individual developers and teams adopting agentic development practices.
