Open sourceTypeScript · ≈73k stars · MIT
OpenSpec
Lightweight spec-driven development (SDD) framework for AI coding assistants.
OpenSpec is an MIT-licensed spec-driven development framework, built for existing codebases and not only new ones. Slash commands such as /opsx:explore, /opsx:propose, /opsx:apply and /opsx:archive guide a coding assistant through each change. A proposal creates a change folder with proposal.md, requirement and scenario specs, design.md and a tasks.md checklist, which the agent then implements. It is distributed on npm as @fission-ai/openspec. It supports 30+ AI assistants, including Claude Code, Cursor, GitHub Copilot, Codex and Amazon Q, and allows third-party schema bundles.
Pros & cons
Each point cites its sources and says what kind of evidence backs it. A second reviewer tried to refute every claim before it was kept.
Pros
- DocsSpecs are Markdown change deltas (ADDED/MODIFIED/REMOVED requirements), which suits brownfield codebases where changes touch existing behavior.[1][2]
- User reportsA third-party comparison reports much lighter output than Spec Kit (about 250 vs 800 lines per change), though the figures are reported rather than measured.[1]
- DocsNeeds no API key or MCP server and supports 30+ coding tools through `/opsx:` commands.[1][2]
- MetadataMIT-licensed, about 73k stars, and the repo keeps its own `openspec/` specs and changes.[1]
Cons
- Independent testChecks are advisory: `validate` checks structure only and `verify` will not block archive, so nothing enforces that code matches the spec.[1]
- User reportsArtifacts are generated in one forward pass, and an open request asks for a cross-artifact review because contradictions between proposal, specs, design and tasks are not caught before apply.[1]
- User reportsSpecs do not update themselves during implementation, and reviewers cite manual spec drift as the main complaint.[1]
- User reportsThe full propose/design/tasks cycle is heavy for small bug fixes, and there is no multi-repo or SSO/SCIM support.[1]
- Best for
- Small, senior teams that want lightweight, reviewable change proposals for agents working in existing codebases.
- Watch out for
- Specs drift unless someone owns archiving and resyncing them after each change; the cited comparison is by a competing spec-tool vendor.
Assessed Oct 29, 2026 · adversarially reviewedSuggest a correction
People
Founder
Creator of OpenSpec, Fission AI
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Connections
Relations from the Harness Hub knowledge graph, as charted in the State of Harness reports.
Maintained by · 1
- Fission AIOrganisation
Built on · 2
- Claude CodeProject
- CodexProject
Sources
Verified Oct 29, 2026