Agent OS is an open-source system by Builder Methods (Brian Casel) for “injecting your codebase standards and writing better specs” for spec-driven development with AI coding agents. MIT licence; ~5.5k GitHub stars, 131 commits, no open issues (GitHub, 2026-09-30). Works with Claude Code, Cursor, Antigravity and similar tools, any language or stack.
Changed since the 2025 version of this note
The original note described a three-layer model (standards in
~/.agent-os/standards/, product in.agent-os/product/, specs in.agent-os/specs/YYYY-MM-DD-feature/) with a base install plus per-tool setup. The current repo README instead lists four capabilities: Discover Standards (extract patterns from your codebase), Deploy Standards (inject relevant ones into context), Shape Spec (plan a feature) and Index Standards. The repo holdscommands/agent-os,profiles/default/globaland scripts. Whether the old three-layer layout still applies in the latest version is unverified; check buildermethods.com/agent-os before relying on the old paths.
Core ideas
- Standards as context: coding standards, tech stack and conventions live in Markdown and are injected into the agent’s context when relevant.
- Spec shaping: turns a vague feature request into a stepwise spec/plan before implementation.
- Markdown-only: everything is plain, version-controlled files, editable by hand.
- Related: design-os (same author) produces UI specs that feed Agent OS; see also speckit, google-conductor.
Pricing
Framework is free/MIT. Builder Methods sells a paid community (Builder Methods Pro) separately.
Sources
- https://github.com/buildermethods/agent-os (accessed 2026-09-30)
Related
- Not to be confused with Agent OS by Sierra (Sierra’s commercial customer-service agent platform), an unrelated product with the same name.