The Claude Code plugin

A scaffolded Substrat project already teaches an agent what it needs: npm create substrat writes the rules, the build playbook, and a session hook that pins the agent to the docs for the kernel version installed there. The plugin exists for the case before that — an agent opened on a directory we did not generate, which has none of it.

claude plugin marketplace add https://substrat.net/marketplace.json
claude plugin install substrat@substrat-run

In Claude Desktop, install it from + → Plugins → Add plugin. Plugins are not available in WSL sessions.

The marketplace also resolves from the repository, if you prefer that form:

claude plugin marketplace add substrat-run/substrat

Both register the same catalog. The URL form downloads one small file; the repository form clones the monorepo, so prefer the URL unless you have a reason not to.

What you get

/substrat — the guided build flow. It works out which of three situations you are in and routes accordingly: an existing Substrat vertical (read its rules and playbook), an empty directory (scaffold one first, then the same), or an existing project that is not a vertical (say so, rather than improvise — Substrat is not a library you add to an app).

A SessionStart hook — silent in any project that is not a Substrat vertical, so it costs you nothing elsewhere. In one that is, it tells the agent where the rules live and which docs slice describes the kernel actually installed. Substrat is pre-1.0 and its interfaces change without notice, so an agent working from pages it cached two minors ago is the expensive failure: confident, plausible, wrong.

What it deliberately does not contain

The build flow itself. That lives in the project, in .substrat/playbook.md, beside the agent rules in AGENTS.md — and that copy is pinned to the kernel version installed there. A copy inside the plugin would go stale on its own schedule, and the rules an agent must not violate are the worst possible thing to be stale about. The plugin routes to the project's copy and never substitutes for it.

This is why the plugin adds nothing to a project you scaffolded: that project already carries its own copy of the skill and the hook. Installing it anyway is harmless — the project's copies win — but it is not something you need to do.

Other tools

The plugin is a Claude Code adapter. Every other client reads the same neutral core, which the scaffold writes into the project directly:

Tool	How it finds the rules
Claude Code	CLAUDE.md, .claude/skills/, .claude/settings.json, .claude/launch.json
Cursor	.cursor/rules/substrat.mdc, .cursor/commands/new-vertical.md
opencode	.opencode/command/new-vertical.md
Codex, Kiro	AGENTS.md, natively — nothing to install

For an agent that has not scaffolded anything and is reading rather than building, substrat.net/llms.txt is the docs index and every page on this site has a .md twin at the same URL.