| name | gdd-live |
| description | Live in-browser design mode. The user picks a DOM element on a running dev server (via the Claude Preview MCP), the agent generates N design variants in one batch, they hot-swap in place through HMR or preview_eval using a data-gdd-variant marker, the user accepts or discards, and the whole pick-generate-accept loop persists to .design/live-sessions so it survives a crash or resume. Use when the user wants to iterate on the look of a live component against a real running server, asks to try variants on a page, or runs the live command with a url; falls back to a screenshot-only degraded mode on harnesses without MCP support. Activates for requests involving in-browser design iteration, picking an element on a dev server, or generating variants with hot-swap. |
| argument-hint | [--variants N] [--resume <session-id>] [url] |
| tools | Read, Write, Edit, Bash, Glob, Grep, Task |
| user-invocable | true |
gdd-live - Live In-Browser Design Mode
Pick a DOM element on a running dev server, generate competing design variants, hot-swap them in place, and accept the winner as a real source edit. Every step persists to .design/live-sessions/<id>.json so the session survives a crash or a later resume.
The browser-side runtime, the harness-mode gate, the session store, the events feed, the post-check, the scope guard, and the bandit feed are all separate modules under scripts/lib/live/. This skill describes the loop and names the module that owns each step; it does not import them.
For the full surface (the Preview MCP tools, the six live_* events, the session file, the bandit feed, degraded mode, the scope guard), see ../../reference/live-mode-integration.md. For the SKILL.md structural contract, see ../../reference/skill-authoring-contract.md.
Arguments
[url] - the page to drive. Optional. When omitted, detect the dev server and use its root.--variants N - how many variants to generate per pick. Default 3.--resume <session-id> - reattach to an in-progress session in .design/live-sessions/.
BOOT
- Probe the Preview MCP per
../../connections/preview.md: ToolSearch({ query: "Claude_Preview" }), then mcp__Claude_Preview__preview_list. Empty ToolSearch means the MCP is not loaded.
- Resolve the harness live mode. The capability signal is
capability_matrix.mcp_support in scripts/lib/manifest/harnesses.json, projected by scripts/lib/live/harness-mode.cjs (liveModeFor(harnessId)). A puppeteer result means full live mode; a degraded result means screenshot-only.
- If
mcp_support is false for this harness, or Preview is unavailable, enter DEGRADED mode and say so plainly: variants are generated and captured as static screenshots, with no in-page hot-swap. Skip the INJECT and PICK steps; generate against the file the user names instead.
- Detect the dev server. Look for Vite, Next, Bun, or a static server (check
package.json scripts plus a preview_list entry). Record the server descriptor on the session.
- Open or create the session via
scripts/lib/live/session-store.cjs (.design/live-sessions/<id>.json). On --resume, load the named session (see RESUME).
INJECT
Inject the browser runtime once. Read RUNTIME_JS from scripts/lib/live/runtime.cjs and evaluate it in the page with mcp__Claude_Preview__preview_eval. The runtime is an idempotent IIFE bound to window.__gddLive, so a re-inject after navigation rebinds the same singleton rather than stacking listeners. It installs the pick handler and the variant-swap helpers, and stamps the live variant on the element via the data-gdd-variant attribute.
PICK
- Arm the picker (
window.__gddLive.pick()), then guide the user to click the target element. Use preview_click and preview_inspect to confirm the element and read its computed styles and bounding box.
- Read the pick report back. Its fields are documented in
pickReportShape (selector, tagName, classList, boundingRect, computedStyle subset, current variant). The selector strategy prefers id, then a data-testid, then a tag plus class plus nth-of-type path.
- Emit a
live_pick event through scripts/lib/live/events.cjs and append a pick entry to the session.
GENERATE (one batch)
- Load the relevant Phase 45 canonical reference index FIRST, so variants are grounded in real guidance: the domain index that matches the picked element (for example
../../reference/spatial.md for layout, ../../reference/interaction.md for components and a11y, ../../reference/color.md for color, ../../reference/typography.md for type, ../../reference/motion.md for animation).
- Generate all N variants in ONE batch (default 3), each a distinct, hypothesis-tagged design direction for the picked element. Do not generate them one at a time.
- For each variant: write the change atomically to the implicated source file, then make it live. With HMR running, the file write is enough; otherwise apply the variant in place with
window.__gddLive.swapVariant({ n, style, html }), which sets data-gdd-variant="n" and applies the variant's style or markup.
POST-CHECK
Run the post-check on each variant via scripts/lib/live/postcheck.cjs, which invokes gdd-detect. Show the findings inline next to each variant. A variant that trips a finding is flagged, NOT auto-rejected: the user still decides. Append a live_postcheck event per variant.
ACCEPT / DISCARD
- ACCEPT one variant: apply the chosen variant as the canonical source edit, and revert the others in the page (
window.__gddLive.revert() on each non-chosen element). Emit a live_accept event and feed the outcome to the design-variants bandit via scripts/lib/live/bandit-feed.cjs (a dev-time signal). Append an accept entry.
- DISCARD: revert every variant in the page back to its captured original and leave the source untouched. Emit a
live_discard event and append a discard entry.
Either way, persist the result through scripts/lib/live/session-store.cjs before continuing.
PERSIST
Every step (boot, pick, generate, post-check, accept, discard) is written to the session file through scripts/lib/live/session-store.cjs as it happens. The on-disk event log uses the pick, generate, accept, discard kinds; the telemetry stream uses the six live_* event types. Writes are atomic, so an interrupted step never leaves a half-written session.
RESUME
With --resume <session-id>, load the named session from .design/live-sessions/. Only an in_progress session is resumable. Offer the user two choices: continue from the last recorded event (report what that was, for example "last pick was the primary button"), or start fresh (open a new session and leave the old one intact). Never silently replay completed events.
SCOPE GUARD
Never write outside the source files implicated by the picked element. Run every proposed write through scripts/lib/live/scope-guard.cjs, which maps the picked selector to its owning source files and rejects edits that fall outside them. If a variant would need a change beyond that scope (a shared token, a parent layout, a new dependency), stop and surface it to the user rather than widening the blast radius.
Constraints
- Do NOT edit files outside the picked element's implicated sources (enforced by the scope guard).
- Do NOT generate variants one at a time; generate the full batch, then swap.
- Do NOT auto-reject a variant on a post-check finding; flag it and let the user decide.
- In DEGRADED mode, state up front that hot-swap is unavailable and fall back to screenshots.
- Persist before every user-facing prompt so a crash never loses accepted work.
LIVE COMPLETE
