diff --git a/apps/rush-mcp-server/package.json b/apps/rush-mcp-server/package.json
index 738c2ccf087..8a562753653 100644
--- a/apps/rush-mcp-server/package.json
+++ b/apps/rush-mcp-server/package.json
@@ -59,6 +59,7 @@
     "@rushstack/rush-sdk": "workspace:*",
     "@rushstack/ts-command-line": "workspace:*",
     "@modelcontextprotocol/sdk": "~1.10.2",
+    "ws": "~8.14.1",
     "zod": "~3.25.76"
   },
   "devDependencies": {
@@ -66,7 +67,8 @@
     "eslint": "~9.37.0",
     "local-node-rig": "workspace:*",
     "typescript": "~5.8.2",
-    "@types/node": "20.17.19"
+    "@types/node": "20.17.19",
+    "@types/ws": "8.5.5"
   },
   "sideEffects": [
     "lib-commonjs/start.js",
diff --git a/apps/rush-mcp-server/src/server.ts b/apps/rush-mcp-server/src/server.ts
index 5eceb116012..1f7cd861d1a 100644
--- a/apps/rush-mcp-server/src/server.ts
+++ b/apps/rush-mcp-server/src/server.ts
@@ -5,6 +5,7 @@ import { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
 
 import {
   type BaseTool,
+  RushBuildStatusTool,
   RushConflictResolverTool,
   RushMigrateProjectTool,
   RushCommandValidatorTool,
@@ -36,6 +37,7 @@ export class RushMCPServer extends McpServer {
   }
 
   private _initializeTools(): void {
+    this._tools.push(new RushBuildStatusTool());
     this._tools.push(new RushConflictResolverTool());
     this._tools.push(new RushMigrateProjectTool(this._rushWorkspacePath));
     this._tools.push(new RushCommandValidatorTool());
diff --git a/apps/rush-mcp-server/src/tools/build-status.tool.ts b/apps/rush-mcp-server/src/tools/build-status.tool.ts
new file mode 100644
index 00000000000..a42742aca09
--- /dev/null
+++ b/apps/rush-mcp-server/src/tools/build-status.tool.ts
@@ -0,0 +1,40 @@
+// Copyright (c) Microsoft Corporation. All rights reserved. Licensed under the MIT license.
+// See LICENSE in the project root for license information.
+
+import { z } from 'zod';
+
+import {
+  fetchBuildStatusAsync,
+  formatBuildStatusSnapshot,
+  type IBuildStatusSnapshot
+} from '../utilities/build-status-client';
+import { BaseTool, type CallToolResult } from './base.tool';
+
+export class RushBuildStatusTool extends BaseTool {
+  public constructor() {
+    super({
+      name: 'rush_get_build_status',
+      description:
+        'Returns the current build status from a running `rush start` session. ' +
+        'Connects to the rush-serve-plugin WebSocket endpoint and returns a snapshot ' +
+        'of all operation statuses. Requires `rush start` to be running.',
+      schema: {
+        port: z.number().describe('The port number where `rush start` is serving'),
+        host: z.string().optional().describe('The hostname (default: localhost)')
+      }
+    });
+  }
+
+  public async executeAsync({ port, host }: { port: number; host?: string }): Promise<CallToolResult> {
+    const snapshot: IBuildStatusSnapshot = await fetchBuildStatusAsync({ port, host });
+
+    return {
+      content: [
+        {
+          type: 'text',
+          text: formatBuildStatusSnapshot(snapshot)
+        }
+      ]
+    };
+  }
+}
diff --git a/apps/rush-mcp-server/src/tools/index.ts b/apps/rush-mcp-server/src/tools/index.ts
index 7fdc2dbd2b1..09f6f209551 100644
--- a/apps/rush-mcp-server/src/tools/index.ts
+++ b/apps/rush-mcp-server/src/tools/index.ts
@@ -2,6 +2,7 @@
 // See LICENSE in the project root for license information.
 
 export { BaseTool, type IBaseToolOptions, type CallToolResult } from './base.tool';
+export { RushBuildStatusTool } from './build-status.tool';
 export { RushMigrateProjectTool } from './migrate-project.tool';
 export { RushProjectDetailsTool } from './project-details.tool';
 export { RushCommandValidatorTool } from './rush-command-validator.tool';
diff --git a/apps/rush-mcp-server/src/utilities/build-status-client.ts b/apps/rush-mcp-server/src/utilities/build-status-client.ts
new file mode 100644
index 00000000000..8af6bd35c00
--- /dev/null
+++ b/apps/rush-mcp-server/src/utilities/build-status-client.ts
@@ -0,0 +1,194 @@
+// Copyright (c) Microsoft Corporation. All rights reserved. Licensed under the MIT license.
+// See LICENSE in the project root for license information.
+
+import WebSocket from 'ws';
+
+/**
+ * URLs for an operation's log files, served by the rush-serve-plugin.
+ */
+export interface ILogFileURLs {
+  text: string;
+  error: string;
+  jsonl: string;
+}
+
+/**
+ * Minimal subset of operation info from the rush-serve-plugin WebSocket protocol.
+ */
+export interface IOperationSummary {
+  name: string;
+  packageName: string;
+  phaseName: string;
+  status: string;
+  startTime: number | undefined;
+  endTime: number | undefined;
+  logFileURLs: ILogFileURLs | undefined;
+}
+
+/**
+ * Session information from the rush-serve-plugin WebSocket protocol.
+ */
+export interface IRushSessionInfo {
+  actionName: string;
+  repositoryIdentifier: string;
+}
+
+/**
+ * A snapshot of the current build status, returned by the WebSocket utility functions.
+ */
+export interface IBuildStatusSnapshot {
+  status: string;
+  operations: IOperationSummary[];
+  sessionInfo?: IRushSessionInfo;
+}
+
+/**
+ * Options for connecting to the rush-serve-plugin WebSocket server.
+ */
+export interface IBuildStatusClientOptions {
+  port: number;
+  host?: string;
+}
+
+/**
+ * WebSocket event message types matching the rush-serve-plugin wire format.
+ * Duplicated here to avoid a runtime dependency on rush-serve-plugin.
+ */
+interface IWebSocketSyncEventMessage {
+  event: 'sync';
+  operations: IOperationSummary[];
+  sessionInfo: IRushSessionInfo;
+  status: string;
+}
+
+type IWebSocketEventMessage =
+  | IWebSocketSyncEventMessage
+  | { event: 'before-execute' | 'status-change' | 'after-execute'; operations: IOperationSummary[] };
+
+function buildWebSocketUrl(options: IBuildStatusClientOptions): string {
+  const host: string = options.host ?? '127.0.0.1';
+  return `wss://${host}:${options.port}/ws`;
+}
+
+function toSnapshot(message: IWebSocketSyncEventMessage): IBuildStatusSnapshot {
+  return {
+    status: message.status,
+    operations: message.operations,
+    sessionInfo: message.sessionInfo
+  };
+}
+
+/**
+ * Formats a build status snapshot into a human-readable string for LLM consumption.
+ */
+export function formatBuildStatusSnapshot(snapshot: IBuildStatusSnapshot): string {
+  const lines: string[] = [];
+
+  lines.push(`Build Status: ${snapshot.status}`);
+
+  if (snapshot.sessionInfo) {
+    lines.push(`Command: ${snapshot.sessionInfo.actionName}`);
+    lines.push(`Repository: ${snapshot.sessionInfo.repositoryIdentifier}`);
+  }
+
+  // Summarize operation statuses
+  const statusCounts: Map<string, number> = new Map();
+  for (const op of snapshot.operations) {
+    statusCounts.set(op.status, (statusCounts.get(op.status) ?? 0) + 1);
+  }
+
+  lines.push('');
+  const total: number = snapshot.operations.length;
+  const summaryParts: string[] = [];
+  for (const [status, count] of statusCounts) {
+    summaryParts.push(`${status}: ${count}`);
+  }
+  lines.push(`Operation Summary: ${total} total`);
+  if (summaryParts.length > 0) {
+    lines.push(`  ${summaryParts.join(', ')}`);
+  }
+
+  // List failed operations
+  const failedOps: IOperationSummary[] = snapshot.operations.filter((op) => op.status === 'Failure');
+  if (failedOps.length > 0) {
+    lines.push('');
+    lines.push('Failed Operations:');
+    for (const op of failedOps) {
+      lines.push(`  - ${op.packageName} (${op.phaseName})`);
+    }
+  }
+
+  // List blocked operations
+  const blockedOps: IOperationSummary[] = snapshot.operations.filter((op) => op.status === 'Blocked');
+  if (blockedOps.length > 0) {
+    lines.push('');
+    lines.push('Blocked Operations:');
+    for (const op of blockedOps) {
+      lines.push(`  - ${op.packageName} (${op.phaseName})`);
+    }
+  }
+
+  return lines.join('\n');
+}
+
+/**
+ * Connects to the rush-serve-plugin WebSocket, receives the initial sync message,
+ * and returns a snapshot of the current build status.
+ */
+export async function fetchBuildStatusAsync(
+  options: IBuildStatusClientOptions
+): Promise<IBuildStatusSnapshot> {
+  const url: string = buildWebSocketUrl(options);
+
+  return new Promise<IBuildStatusSnapshot>((resolve, reject) => {
+    const ws: WebSocket = new WebSocket(url, { rejectUnauthorized: false });
+    let settled: boolean = false;
+
+    const connectionTimeout: NodeJS.Timeout = setTimeout(() => {
+      if (!settled) {
+        settled = true;
+        ws.close();
+        reject(new Error(`Connection to rush start timed out after 10000ms.`));
+      }
+    }, 10000);
+
+    function settle(action: () => void): void {
+      if (!settled) {
+        settled = true;
+        clearTimeout(connectionTimeout);
+        action();
+      }
+    }
+
+    ws.on('error', (err: Error) => {
+      settle(() =>
+        reject(
+          new Error(
+            `Cannot connect to rush start on port ${options.port}. Ensure \`rush start\` is running. (${err.message})`
+          )
+        )
+      );
+    });
+
+    ws.on('close', () => {
+      settle(() =>
+        reject(
+          new Error(`Connection to rush start on port ${options.port} closed before receiving build status.`)
+        )
+      );
+    });
+
+    ws.on('message', (data: WebSocket.Data) => {
+      try {
+        const message: IWebSocketEventMessage = JSON.parse(data.toString());
+        if (message.event === 'sync') {
+          settle(() => resolve(toSnapshot(message)));
+          ws.close();
+        }
+      } catch (parseError: unknown) {
+        ws.close();
+        settle(() => reject(new Error(`Failed to parse WebSocket message: ${parseError}`)));
+      }
+    });
+  });
+}
diff --git a/common/changes/@rushstack/mcp-server/user-frags51-start-mcp_2026-03-21-00-14.json b/common/changes/@rushstack/mcp-server/user-frags51-start-mcp_2026-03-21-00-14.json
new file mode 100644
index 00000000000..3cfe487ef25
--- /dev/null
+++ b/common/changes/@rushstack/mcp-server/user-frags51-start-mcp_2026-03-21-00-14.json
@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@rushstack/mcp-server",
+      "comment": "Build tool for rush start",
+      "type": "minor"
+    }
+  ],
+  "packageName": "@rushstack/mcp-server"
+}
\ No newline at end of file
diff --git a/common/config/subspaces/default/pnpm-lock.yaml b/common/config/subspaces/default/pnpm-lock.yaml
index dd1378b412d..4032b37513f 100644
--- a/common/config/subspaces/default/pnpm-lock.yaml
+++ b/common/config/subspaces/default/pnpm-lock.yaml
@@ -447,6 +447,9 @@ importers:
       '@rushstack/ts-command-line':
         specifier: workspace:*
         version: link:../../libraries/ts-command-line
+      ws:
+        specifier: ~8.14.1
+        version: 8.14.2
       zod:
         specifier: ~3.25.76
         version: 3.25.76
@@ -457,6 +460,9 @@ importers:
       '@types/node':
         specifier: 20.17.19
         version: 20.17.19
+      '@types/ws':
+        specifier: 8.5.5
+        version: 8.5.5
       eslint:
         specifier: ~9.37.0
         version: 9.37.0