Creating an Apex Rest API and using it as a custom tool in custom mcp server
🛠Prerequisites
- A Salesforce Account (Developer Edition or Sandbox recommended).
- Postman installed on your machine.
- Basic understanding of REST APIs.
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:
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 (Now External Client App) in Salesforce
This acts as the doorway for Postman to enter Salesforce.
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Log in to Salesforce Setup (gear icon → Setup).
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In Quick Find, search for App Manager.
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Click New External Client App (top-right).
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Fill in:
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External Client App Name
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API Name
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Contact Email
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Check Enable OAuth Settings.
- Set Callback URL (Use the standard Postman callback)
https://oauth.pstmn.io/v1/callback
- In Selected OAuth Scopes, add:
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Access and manage your data (api)
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Perform requests on your behalf at any time (refresh_token, offline_access)
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These scopes let your app call Salesforce APIs and get a refresh token.
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Save the external client app and wait ~10 minutes for it to fully propagate.
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Once saved, open the app’s detail page.
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Get SF_CLIENT_ID and SF_CLIENT_SECRET
On your external client app’s detail screen:
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Consumer Key → this is your SF_CLIENT_ID
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Consumer Secret → this is your SF_CLIENT_SECRET
Salesforce labels them Consumer Key and Consumer Secret respectively.
4) Set Environment Variables
