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Contracts are the shared definitions that we define in-order to get the type-safety from the Rest API. Example of a contract: 
import { initContract } from "@ts-rest/core";
import { z } from "zod";

const c = initContract();

export const helloContract = c.router({
  getHello: {
    method: "GET",
    path: "/hello",
    responses: {
      200: z.object({
        response: z.string(),
      }),
      500: z.object({
        response: z.string(),
      }),
    },
    summary: "Echo Hello",
  },
});

​
Adding a contract

You can add a contract by simply creating another file in the /packages/contract folder. Then import it in the index.ts file of the folder and add it to the super contract like this: 
import { AppRouter, initContract } from "@ts-rest/core";
import { textContract } from "./text";
import { helloContract } from "./hello";
import { newContract } from "./new";

const c = initContract();
export const superContract = c.router({
  text: textContract,
  hello: helloContract
  new: newContract // This is the new contract
});

​
Contract Implementation

Now we need to implement this contract in the backend. By default we have an express apps, so we will navigate to: apps/backend/src/api/routes and create a new route. We now will have to implement all the functions in the contract that we specified in the shared package in the previous step. Example of contract implementation: 
import { initServer } from "@ts-rest/express";
import Container from "typedi";
import { Logger } from "winston";
import { z } from "zod";

import { superContract } from "@repo/contract";

import HelloService from "../../services/hello";

export default (server: ReturnType<typeof initServer>) => {
  const logger: Logger = Container.get("logger");
  const helloServiceInstance: HelloService = Container.get(HelloService);

  return server.router(superContract.hello, {
    getHello: {
      handler: async () => {
        try {
          const hello = helloServiceInstance.generateHello();
          return {
            status: 200,
            body: {
              response: hello,
            },
          };
        } catch (e) {
          logger.error(e);
          return {
            status: 500,
            body: {
              response: "Internal Server Error",
            },
          };
        }
      },
    },
  });
};
You can break out all the functionalities related to an entity in the services folder.
Learn more about contracts on the TS-Rest express adapter documentation.
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