chapplin-mcp-app-builder

name	chapplin-mcp-app-builder
description	Build and debug MCP App-enabled tools in existing projects scaffolded by create-chapplin. Use when extending tools/*.tsx with defineTool and defineApp<typeof tool>, wiring structuredContent and _meta for UI data flow, handling runtime differences across react/preact/solid/hono targets, or troubleshooting chapplin preview and host-context behavior.

Chapplin MCP App Builder

Overview

Use this skill to extend an existing create-chapplin project with new MCP App-enabled tools while preserving template conventions and minimal diffs.

Quick Workflow

1. Confirm the project matches the baseline in references/project-baseline.md.
2. Detect the framework target from vite.config.ts and chapplin({ target }).
3. Implement defineTool first, then implement defineApp<typeof tool>.
4. Import useApp from chapplin/<target> only when host actions are needed.
5. Put machine-facing data in structuredContent and UI-only payload in _meta.
6. Validate with dev preview and tool-call/UI rendering checks.

Framework/Runtime Selection Rule

1. Read vite.config.ts.
2. Resolve target from chapplin({ target: "..." }).
3. Follow references/framework-deltas.md for plugin, JSX runtime, and useApp import mapping.
4. Keep existing style patterns in the same target template.

Implementation Guardrails

• Do not edit generated artifacts such as dist/, .chapplin/types, or other build outputs.
• Do not change HTTP/STDIO transport structure in src/index.ts unless explicitly requested.
• Keep diffs focused on the requested tool/app behavior.
• Match existing naming, schema style, and JSX conventions in the current project.

Validation Checklist

1. Run npm run dev and open the chapplin preview UI.
2. Execute the target tool once and confirm UI renders expected state.
3. Confirm initial empty state is handled (props.output may be undefined before first result).
4. Run project checks (typically npm run build and any local test/check scripts).
5. Re-check framework-specific assumptions against references/framework-deltas.md.

Reference File Map

• Baseline project shape and registration flow: references/project-baseline.md
• Target-specific runtime differences: references/framework-deltas.md
• Reusable implementation patterns: references/implementation-recipes.md
• Common failures and fixes: references/troubleshooting.md