skill-builder

skill-builder

Author new universal skills from natural-language prompts across any agent host (Claude Code, Cursor, Codex, Gemini CLI, Windsurf, OpenCode, and the rest of the 50+ agents in the vskill registry).

What this skill does

skill-builder is a cross-tool authoring meta-skill. When the host agent sees a trigger phrase (see frontmatter description), this skill takes over and produces a new SKILL.md — emitted for every target agent, not just the one currently invoking it. The emitted skills carry an x-sw-schema-version: 1 marker so future tooling can evolve the format without breaking older installs.

It does this by delegating to the real generator via a three-path fallback chain:

• Path A — vskill skill CLI (preferred). The CLI owns the full authoring pipeline: prompt parsing, target-agent lowering, divergence report, security scan, and disk write.
• Path B — vskill Studio (browser). When the CLI is not on PATH but the npm package is present (e.g. a project-local install), start the eval server and walk the user through the Studio UI.
• Path C — Anthropic skill-creator (Claude Code only fallback). Delegate to the built-in Anthropic authoring skill. This produces a single Claude-flavored SKILL.md with no universal targets, so we log the degradation so users know what they're getting.

Each path is tried in order; the first one whose detection check succeeds wins. If none match, we emit a remediation message and stop.

Detection script

The host agent runs this snippet (or the equivalent) before authoring anything. Return on the first path whose probe exits 0.

# Path A: vskill CLI on PATH
if which vskill >/dev/null 2>&1; then
  # Invoke the CLI. --targets is optional; default is the full
  # universal set. --prompt is the user's natural-language request.
  vskill skill new --prompt "<USER_PROMPT>" [--targets=<csv>]
  exit $?
fi

# Path B: vskill package resolvable but no CLI on PATH
if node -e "require.resolve('vskill')" >/dev/null 2>&1; then
  vskill eval serve
  echo "[skill-builder] open the URL printed above and use the Studio 'New skill' flow"
  exit 0
fi

# Path C: Claude Code host with Anthropic skill-creator installed
if [ "${SW_HOST_AGENT:-claude-code}" = "claude-code" ] \
   && test -d "$HOME/.claude/skills/skill-creator"; then
  echo "[skill-builder] fallback mode — universal targets not emitted; install vskill for universal support"
  # Delegate to the Anthropic built-in. The host agent will route
  # the original user prompt into skill-creator.
  exit 0
fi

# Nothing matched — print remediation and fail loudly.
cat <<'EOF'
[skill-builder] no authoring backend available. Install one of:

  npm install -g vskill          # preferred — universal targets
  claude plugin install skill-creator   # Claude Code only, no universal emit

EOF
exit 1