Creating an Apex Rest API and using it as a custom tool in Custom MCP Server

Creating an Apex Rest API and using it as a custom tool in custom mcp server

Here is an end-to-end implementation that:

✅ Exposes a Salesforce custom REST API that returns object field metadata

✅ Calls it from your custom MCP stdio server (Node.js)

✅ Makes it available to Copilot Agent

This solution uses Apex REST for object describe and jsforce in your MCP server to authenticate & fetch the results.

1) Apex REST Endpoint (Salesforce)

Create this Apex class in your Salesforce org. It returns a list of field metadata (name, label, type) for any object.

Save as ObjectFieldsController.cls:

@RestResource(urlMapping='/ObjectFields/*')
global with sharing class ObjectFieldsController {

    global class FieldInfo {
        public String name;
        public String label;
        public String type;
    }

    @HttpGet
    global static List<FieldInfo> getObjectFields() {
        String sObjectName = RestContext.request.requestURI.substring(
            RestContext.request.requestURI.lastIndexOf('/') + 1
        );

        if (String.isBlank(sObjectName)) {
            return new List<FieldInfo>();
        }

        Map<String, Schema.SObjectField> fieldMap =
            Schema.getGlobalDescribe().get(sObjectName).getDescribe().fields.getMap();

        List<FieldInfo> output = new List<FieldInfo>();
        for (String key : fieldMap.keySet()) {
            Schema.DescribeFieldResult d = fieldMap.get(key).getDescribe();
            FieldInfo info = new FieldInfo();
            info.name = d.getName();
            info.label = d.getLabel();
            info.type = String.valueOf(d.getType());
            output.add(info);
        }
        return output;
    }
}

This returns an array of simple objects with field name, label, and type. Apex REST requires a concrete return type (not Object) so we define FieldInfo.

2) MCP Server (Node.js)

This is your MCP stdio server that Copilot can call.

Install Required Packages:

npm install mcp-use jsforce

server.js
#!/usr/bin/env node
import { createMCPServer } from "mcp-use/server";
import jsforce from "jsforce";

// Salesforce connection info — set via environment variables
const {
  SF_LOGIN_URL,
  SF_USERNAME,
  SF_PASSWORD,
  SF_CLIENT_ID,
  SF_CLIENT_SECRET,
  SF_REFRESH_TOKEN
} = process.env;

// Define your custom tool
const tools = {
  getObjectFields: async ({ input }) => {
    try {
      const { objectName } = input;
      if (!objectName) {
        return {
          result: { error: "Input must include objectName" }
        };
      }

      const conn = new jsforce.Connection({
        loginUrl: SF_LOGIN_URL || "https://login.salesforce.com",
        clientId: SF_CLIENT_ID,
        clientSecret: SF_CLIENT_SECRET,
        refreshToken: SF_REFRESH_TOKEN
      });

      if (SF_REFRESH_TOKEN) {
        await conn.refreshToken(SF_REFRESH_TOKEN);
      } else {
        await conn.login(SF_USERNAME, SF_PASSWORD);
      }

      const result = await conn.apex.get(
        `/ObjectFields/${encodeURIComponent(objectName)}`
      );

      if (!Array.isArray(result)) {
        return {
          result: { error: "Unexpected response format from Salesforce" }
        };
      }

      const summary = `Object ${objectName} has ${result.length} fields: ` +
        result.map(f => `${f.name} (${f.type})`).join(", ");

      return {
        result: {
          text: summary,
          fields: result
        }
      };
    } catch (err) {
      return {
        result: {
          error: err.message
        }
      };
    }
  }
};

// Start stdio MCP server
createMCPServer({ tools });
// keep alive
setInterval(() => {}, 1e9);

3) Create a Connected App (New External Client App) in Salesforce

• Log in to Salesforce Setup (gear icon → Setup).

• In Quick Find, search for App Manager.

• Click New External Client App (top-right).

• Fill in:

  External Client App Name

  API Name

  Contact Email

Check Enable OAuth Settings.

Set Callback URL (for now you can use something like):

https://login.salesforce.com/services/oauth2/success

(It’s required, even if you won’t use it directly.)

• In Selected OAuth Scopes, add:

  • Access and manage your data (api)

  • Perform requests on your behalf at any time (refresh_token, offline_access)

These scopes let your app call Salesforce APIs and get a refresh token.

• Save the connected app and wait ~10 minutes for it to fully propagate.

• Once saved, open the app’s detail page.

  Get SF_CLIENT_ID and SF_CLIENT_SECRET

On your connected app’s detail screen:

✔ Consumer Key → this is your SF_CLIENT_ID

✔ Consumer Secret → this is your SF_CLIENT_SECRET

Salesforce labels them Consumer Key and Consumer Secret respectively.

3) Get a Refresh Token (SF_REFRESH_TOKEN)

Use Postman (easier for many users)

• In Postman, create a new http request.

• Go to the Authorization tab.

• Make sure no collection is selected in collections tab

• Select OAuth 2.0 → Get New Access Token.

• Fill in:

  • Token Name: Personal API

  • Grant Type: Authorization Code(With PKCE)

  • Callback URL: same as in your connected app or use Authorize using browser

  • Auth URL: https://login.salesforce.com/services/oauth2/authorize

  • Access Token URL: https://login.salesforce.com/services/oauth2/token

  • Client ID: your Consumer Key

  • Client Secret: your Consumer Secret

  • Code Challenge Method: SHA-256

  • Scope: api refresh_token

  Click Get New Access Token.

  Log in and authorize.

Postman will show you the Refresh Token which you can copy.

This method uses Salesforce’s OAuth and gives you both tokens (access and refresh) in a GUI.

4) Set Environment Variables

Store your Salesforce credentials securely in user settings:

Update .vscode/mcp.json

mcp.json
{
  "servers": {
    "Custom MCP": {
      "type": "stdio",
      "command": "node",
      "args": ["server.js"],
      "cwd": "${workspaceFolder}/my-mcp-server"
    }
  }
}

✔ Copilot/Agentforce will spawn your custom MCP server via stdio

✔ Ensure you restart VS Code after saving this

5) Execute this command in Copilot/Agentforce to test the API

Call the tool getObjectFields for Account

🎉 Result

You now have a fully working custom Salesforce API + MCP tool that:

✨ Calls an Apex REST endpoint

✨ Returns Salesforce field metadata

✨ Responds in natural language via Copilot/Agentforce

Also explore below links:

How to install the Standard MCP Server Part 1

How to install the Custom MCP Server Part 2