FeelFlow Open-Sources ff-dev-toolkit, the Official Implementation of AI Spec-Driven Development

On July 11, 2026, FeelFlow released a development plugin it had developed and used internally as open-source software on GitHub under Apache License 2.0. The plugin is now called ff-dev-toolkit; its name at the time of the release was dev-toolkit.

Initially released as a Claude Code plugin, it now also supports Codex.

The Official Implementation of AI Spec-Driven Development

ff-dev-toolkit is the official implementation of AI Spec-Driven Development (AI-SDD), a methodology that treats specifications as input to AI. It combines Skills, MCP (Model Context Protocol) servers, and other components to support:

• Initializing development documents
• Gate management across five stages: requirements → specifications → planning → implementation → verification
• Assessing the impact of changes
• Cross-reviews by multiple AI tools
• Capturing and reusing development knowledge

Repository and Installation

• Repository: github.com/feel-flow/ff-dev-toolkit
• License: Apache License 2.0
• Original release documentation: README from July 11, 2026

For Claude Code, install the plugin using its current name:

claude plugin marketplace add feel-flow/ff-dev-toolkit
claude plugin install ff-dev-toolkit@ff-dev-toolkit

See the repository README for prerequisites and the latest compatibility information.

Related Books

ff-dev-toolkit is the implementation covered by the official implementation reference in AI仕様駆動開発 公式ガイド (the official AI-SDD guide, in Japanese). The methodology is also presented in AI仕様駆動開発: AIエージェント開発の新常識 by FeelFlow CTO Futoshi Okazaki.

This article records the release on July 11, 2026. The current name, supported environments, installation instructions, and book information reflect the information available when this article was added on November 2, 2026.