Audience: operators choosing an install path, migrating between forms, or upgrading an existing project. Time to read: 10 min. Last updated: 2026-06-05.
Mycelium runs as a Claude Code plugin (post-v0.20.0) and as a legacy npx-degit install (pre-v0.20.0, deprecated). This page covers all install paths, the migration between them, upgrading, and self-hosted runtimes.
Inside Claude Code:
/plugin marketplace add haabe/mycelium
/plugin install mycelium@haabe-mycelium
/mycelium:start
/mycelium:start is the recommended first-run command. It composes /mycelium:setup (project-state directories under .claude/) and /mycelium:interview (10-minute discovery on your idea) into one invocation, with a short welcome to bridge the install-to-value gap. Both sub-skills remain invocable directly if you prefer piecewise. None of the steps touch your project root files (CLAUDE.md, README, LICENSE). Idempotent: re-running on an initialized project routes to /mycelium:diamond-assess instead.
Skills are namespaced (/mycelium:<name>) per Anthropic's plugin convention. Use /myc<Tab> to expand the prefix, or invoke in prose ("run mycelium start", "have mycelium assess current state"). Claude Code routes either form.
For a step-by-step first-run walkthrough, see get-started.md.
The npx degit haabe/mycelium install path is no longer supported for new installs. As of v0.20.x, framework reference content (skills, hooks, engine, schemas, scripts) lives in the plugin cache, not in the user's project. A fresh npx degit would land an empty .claude/ with no skills to invoke and no hooks to fire.
Existing legacy installs continue to work locally. To migrate to plugin form, see the migration section below. To recover from a broken legacy refresh, see migration.md#recovering-from-a-broken-legacy-refresh.
Legacy removal was scheduled for v0.21.0 (target 2026-06-09). That did not happen — v0.21.0 shipped 2026-05-09 and .claude/manifest.yml and upgrade.sh are both still present as of 0.66.x. The legacy tree is unmaintained rather than removed; treat plugin form as the only supported install and npx degit as non-functional.
If you already installed Mycelium via npx degit and want to switch to plugin form, your project state (canvas, diamonds, memory, decision log) is preserved. The agent-driven path:
/plugin marketplace add haabe/mycelium
/plugin install mycelium@haabe-mycelium
/mycelium:migrate-from-legacy
The skill walks through detection, plugin verification, the explicit "what will and will not change" preview, the migration script, and verification. Migration is reversible via git (git reset --hard HEAD before committing).
Or run the script directly: bash .claude/scripts/upgrade.sh --migrate-to-plugin. Use --check-migration to see which form your project is on without making changes. Full guide: migration.md.
Heads-up if your install is older than v0.20.10: the
--migrate-to-pluginflag was added in v0.20.10. If your local.claude/scripts/upgrade.shpredates it, the script will treat the flag as a version arg and fail with "Failed to pull upstream. Check version/tag exists: --migrate-to-plugin". Fix: runbash .claude/scripts/upgrade.sh(no args) once first to refresh yourupgrade.shfrom upstream main, then re-invoke with the flag. Surfaced during the maintainer's own self-migration on 2026-05-09.
Mycelium is not a software library; it's instructions that reshape agent behavior. Upgrading replaces framework files while preserving your project state.
Plugin form (recommended, post-v0.20.0):
/plugin update mycelium@haabe-mycelium
Plugin auto-update is on by default for the official-style marketplace. Manual update: /plugin marketplace update haabe-mycelium followed by /reload-plugins.
Legacy form:
bash .claude/scripts/upgrade.sh # latest
bash .claude/scripts/upgrade.sh v0.12.0 # specific versionAfter upgrading, run /mycelium:diamond-assess (plugin form) or /diamond-assess (legacy) to see your work through the new version's lens.
Mycelium runs on opencode with local models (Ollama, LM Studio) for users who want to escape Claude Code's pricing model. The substrate ports verbatim; three runtime safety mechanisms degrade to model-following-instructions rather than structural enforcement. Honest support matrix and setup steps: integrations/opencode.md.