Nts Add MCP

Add MCP entry point to an existing project

Use when

• User wants Claude Desktop, Cursor, or any MCP-compatible AI client to interact with the app.
• User says "expose this to MCP" / "add MCP tools" / "let AI query the data".
• User invokes /nts-add-mcp.

Prerequisite check

This skill requires Better Auth to be wired (the OAuth provider behind the MCP plugin). Before doing anything else:

1. Check for src/server/auth/index.ts — abort if missing.
2. Check that Better Auth is in package.json dependencies — abort if missing.

If auth isn't wired, tell the user to run /nts-add-auth first.

What this skill does

1. Adds the mcp plugin to the Better Auth config.
2. Creates src/app/api/mcp/route.ts — the Streamable HTTP endpoint, wrapped in withMcpAuth.
3. Creates src/app/.well-known/oauth-authorization-server/route.ts and src/app/.well-known/oauth-protected-resource/route.ts for discovery.
4. Creates src/server/mcp/registry.ts — the tool dispatch table.
5. Creates src/server/mcp/tools/_example-search.ts — one worked tool wrapping a service.
6. Creates a Prisma migration to add the three OAuth tables (oauth_application, oauth_access_token, oauth_consent).
7. Updates CLAUDE.md to document the MCP entry point.
8. Adds dev tunnel instructions to the README (Claude Desktop only accepts HTTPS connectors).

Confirmation flow

Before writing:

1. Verify project structure (Better Auth present, src/app/api/ exists).
2. Pick the example tool — default is "search the first table the user has". If unclear, pick example_search against the _example module if it exists.
3. Show the file list. Confirm.

File contents

Update src/server/auth/index.ts

Find the plugins: [...] array and add mcp({ loginPage: "/login" }):

import { mcp } from "better-auth/plugins/mcp";

export const auth = betterAuth({
  // ... existing config
  plugins: [
    // ... existing plugins
    mcp({ loginPage: "/login" }),
  ],
});

Create src/app/api/mcp/route.ts

Use the template at assets/mcp-route.ts.template from the scaffold-internal-tool skill (the content is portable — just substitute {{IF_*}} for the present case).

Create src/app/.well-known/oauth-authorization-server/route.ts

import { auth } from "@/server/auth";

export async function GET() {
  return Response.json(await auth.api.getMcpOAuthMetadata());
}

(Better Auth's mcp plugin exposes this metadata helper — version may differ; check better-auth/plugins/mcp exports if the name changed.)

Create src/server/mcp/registry.ts and src/server/mcp/tools/_example-search.ts

Use the templates mcp-registry.ts.template and mcp-tool-example.ts.template from the scaffold-internal-tool skill.

Create migration

Run:

pnpm prisma migrate dev --name add_mcp_oauth_tables

Better Auth's CLI can generate the Prisma model declarations for the OAuth tables — see Better Auth docs for the current command (typically npx @better-auth/cli generate).

Update CLAUDE.md

Add to the stack section:

- **MCP:** Streamable HTTP at `/api/mcp`, Better Auth `mcp` plugin as OAuth provider. Tools in `src/server/mcp/tools/`.

Add to "Useful commands":

- Local MCP testing: Claude Desktop only accepts HTTPS connectors. Tunnel via `cloudflared tunnel --url http://localhost:3000` and update `BETTER_AUTH_URL` + `next.config.ts` `allowedDevOrigins` to the tunnel host while testing.

How to add more tools later

Tell the user (and put this in CLAUDE.md too):

To add an MCP tool:

1. Create src/server/mcp/tools/<tool-name>.ts exporting { description, inputSchema, handler }.
2. The handler should validate its input via the same Zod schema as the corresponding tRPC procedure, then call the service method with the OAuth-derived userId.
3. Register in src/server/mcp/registry.ts.
4. Restart pnpm dev. Test from Claude Desktop's MCP servers UI.

Verification

pnpm install
pnpm prisma migrate dev
pnpm tsc --noEmit
pnpm build

Don't try to actually exercise the MCP flow from this session — that requires an MCP client. Tell the user how to test it manually.