---

name: developing-backend description: | Backend development with tRPC v11, Prisma v6, and Neon PostgreSQL. Use when creating API routes, database operations, validation, or server logic. Triggers: "tRPC", "router", "API", "endpoint", "database", "Prisma", "query", "mutation", "backend".

Backend Development

Specialized guidance for type-safe API development with tRPC, Prisma ORM, and PostgreSQL.

Critical Rules

1. Validate All Inputs: Use Zod schemas on every procedure
2. Proper Error Codes: Use TRPCError with correct HTTP semantics
3. Select Only Needed Fields: Never fetch entire records unnecessarily
4. Auth/Authz Checks: Protected procedures + resource ownership verification
5. No Console Logs: Use TRPCError, not console.log

Router Location

Copysrc/server/routers/_app.ts  # Router registry
src/server/routers/*.ts     # Feature routers (lowercase)
src/server/trpc.ts          # Core setup, middleware

Standard Router Pattern

Copyimport { z } from 'zod';
import { createTRPCRouter, publicProcedure, protectedProcedure } from '../trpc';
import { TRPCError } from '@trpc/server';

export const featureRouter = createTRPCRouter({
  // Public query
  getAll: publicProcedure
    .query(async ({ ctx }) => {
      return await ctx.db.feature.findMany({
        select: { id: true, title: true },
        orderBy: { createdAt: 'desc' },
      });
    }),

  // Query with input
  getById: publicProcedure
    .input(z.object({ id: z.string().uuid() }))
    .query(async ({ ctx, input }) => {
      const item = await ctx.db.feature.findUnique({
        where: { id: input.id },
      });

      if (!item) {
        throw new TRPCError({
          code: 'NOT_FOUND',
          message: 'Feature not found',
        });
      }

      return item;
    }),

  // Protected mutation
  create: protectedProcedure
    .input(z.object({
      title: z.string().min(1).max(255),
    }))
    .mutation(async ({ ctx, input }) => {
      return await ctx.db.feature.create({
        data: {
          ...input,
          userId: ctx.session.user.id,
        },
      });
    }),
});

Error Codes

Reference Files

• Validation patterns: See VALIDATION.md
• Query optimization: See QUERIES.md
• Auth patterns: See AUTH.md

Pre-Completion Checklist

Copy- [ ] All inputs validated with Zod
- [ ] Authentication checks on protected procedures
- [ ] Authorization checks for resource ownership
- [ ] TRPCError with proper codes
- [ ] Database queries optimized (select only needed)
- [ ] No console.log statements
- [ ] TypeScript compiles (`npm run compile`)