Fission-AI/OpenSpec

A Spec-Driven Development toolkit for AI coding assistants — structured specifications + planning artifacts that guide agent execution.

What it is

A TypeScript-based methodology + tooling package for Spec-Driven Development (SDD) targeted at AI coding workflows. Provides spec templates, planning scaffolds, and integration points for Claude Code, Cursor, and similar agent surfaces. Operates in the same space as github/spec-kit — both pitch structured specs as the bridge between product intent and AI-generated code. MIT-licensed.

Key features

Spec templates for product intent, design decisions, and implementation plans.
Context-engineering guidance for AI agents — what to give them, in what shape.
TypeScript CLI for spec management.
Integration with major coding-agent surfaces.
Companion site at openspec.dev.
MIT-licensed.

Tech stack

TypeScript primary.
CLI distributed via npm.

When to reach for it

You want a third-party SDD methodology rather than GitHub's spec-kit.
You're comparing the SDD-tooling space and want hands-on exposure to multiple options.
You're already deep into Cursor / Claude Code and want a framework-light spec layer.

When not to reach for it

You want first-party GitHub tooling integration — github/spec-kit is closer-fit.
You don't want a methodology framework — plain Markdown specs in your repo work.

Maturity signal

52k stars, 4k forks, MIT, actively maintained. The SDD-tooling category is young; multiple frameworks competing for the same niche.

Alternatives

github/spec-kit — first-party from GitHub.
Linear / Notion + manual prompts — use when you don't want a methodology framework.

Wiki: Fission-AI/OpenSpec