diff --git a/react-packager/src/Activity/Types.js b/react-packager/src/Activity/Types.js
index 47332bf1..cc996c74 100644
--- a/react-packager/src/Activity/Types.js
+++ b/react-packager/src/Activity/Types.js
@@ -11,16 +11,26 @@
  */
 'use strict';
 
-export type EventOptions = {
+export type Options = {
   telemetric?: boolean,
   silent?: boolean,
+  displayFields?: Array<string> | true,
 };
 
-export type Event = {
-  id: number,
-  startTimeStamp: [number, number],
-  durationMs?: number,
-  name: string,
-  data?: any,
-  options: EventOptions,
+type EventFieldDescriptor = {
+  type: 'int' | 'normal',
+  value: number | string | boolean,
+};
+
+export type NormalisedEventData = {[key: string]: EventFieldDescriptor};
+
+export type EventData = {[key: string]: number | string | boolean};
+
+export type Event = {
+  data: NormalisedEventData,
+  durationMs?: number,
+  id: number,
+  name: string,
+  options: Options,
+  startTimeStamp: [number, number],
 };
diff --git a/react-packager/src/Activity/__tests__/Activity-test.js b/react-packager/src/Activity/__tests__/Activity-test.js
index 5edadd98..a8153426 100644
--- a/react-packager/src/Activity/__tests__/Activity-test.js
+++ b/react-packager/src/Activity/__tests__/Activity-test.js
@@ -32,7 +32,7 @@ describe('Activity', () => {
       const EVENT_NAME = 'EVENT_NAME';
       const DATA = {someData: 42};
 
-      Activity.startEvent(EVENT_NAME, DATA);
+      Activity.startEvent(EVENT_NAME, DATA, {displayFields: ['someData']});
       jest.runOnlyPendingTimers();
 
       // eslint-disable-next-line no-console-disallow
@@ -41,7 +41,7 @@ describe('Activity', () => {
       const consoleMsg = console.log.mock.calls[0][0];
       expect(consoleMsg).toContain('START');
       expect(consoleMsg).toContain(EVENT_NAME);
-      expect(consoleMsg).toContain(JSON.stringify(DATA));
+      expect(consoleMsg).toContain('someData: 42');
     });
 
     it('does not write the "START" phase of silent events to the console', () => {
@@ -61,7 +61,7 @@ describe('Activity', () => {
       const EVENT_NAME = 'EVENT_NAME';
       const DATA = {someData: 42};
 
-      const eventID = Activity.startEvent(EVENT_NAME, DATA);
+      const eventID = Activity.startEvent(EVENT_NAME, DATA, {displayFields: ['someData']});
       Activity.endEvent(eventID);
       jest.runOnlyPendingTimers();
 
@@ -71,7 +71,7 @@ describe('Activity', () => {
       const consoleMsg = console.log.mock.calls[1][0];
       expect(consoleMsg).toContain('END');
       expect(consoleMsg).toContain(EVENT_NAME);
-      expect(consoleMsg).toContain(JSON.stringify(DATA));
+      expect(consoleMsg).toContain('someData: 42');
     });
 
     it('does not write the "END" phase of silent events to the console', () => {
diff --git a/react-packager/src/Activity/formatData.js b/react-packager/src/Activity/formatData.js
new file mode 100644
index 00000000..a4c0f586
--- /dev/null
+++ b/react-packager/src/Activity/formatData.js
@@ -0,0 +1,42 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ *
+ */
+'use strict';
+
+import type {Event} from './Types';
+
+function getDataString(event: Event): string {
+  const {options, data} = event;
+  const {displayFields} = options;
+
+  if (!Object.keys(data).length ||
+    !(Array.isArray(displayFields) || displayFields === true)) {
+    return '';
+  }
+
+  const fields = Array.isArray(displayFields) ? displayFields : Object.keys(data);
+  const dataList = fields.map(field => {
+    if (data[field] === undefined) {
+      throw new Error(`"${field}" is not defined for event ""${event.name}"!`);
+    }
+    return `${field}: ${data[field].value.toString()}`;
+  });
+
+  let dataString = dataList.join(' | ');
+
+  if (dataString) {
+    dataString = `  ${dataString}  `;
+  }
+
+  return dataString;
+}
+
+module.exports = getDataString;
diff --git a/react-packager/src/Activity/index.js b/react-packager/src/Activity/index.js
index 2339090f..4ad5ad05 100644
--- a/react-packager/src/Activity/index.js
+++ b/react-packager/src/Activity/index.js
@@ -11,11 +11,12 @@
  */
 'use strict';
 
-import type {EventOptions} from './Types';
-import type {Event} from './Types';
+import type {Event, EventData, Options} from './Types';
 
 const chalk = require('chalk');
 const events = require('events');
+const formatData = require('./formatData');
+const normaliseEventData = require('./normaliseEventData');
 
 let ENABLED = true;
 let UUID = 1;
@@ -23,24 +24,21 @@ let UUID = 1;
 const EVENT_INDEX: {[key: number]: Event} = Object.create(null);
 const EVENT_EMITTER = new events.EventEmitter();
 
-function startEvent(
-  name: string,
-  data: any = null,
-  options?: EventOptions = {},
-): number {
+function startEvent(name: string, data: EventData = {}, options: Options = {}): number {
   if (name == null) {
     throw new Error('No event name specified!');
   }
 
   const id = UUID++;
   EVENT_INDEX[id] = {
+    data: normaliseEventData(data),
     id,
-    startTimeStamp: process.hrtime(),
-    name,
-    data,
     options,
+    name,
+    startTimeStamp: process.hrtime(),
   };
   logEvent(id, 'startEvent');
+
   return id;
 }
 
@@ -74,12 +72,11 @@ function logEvent(id: number, phase: 'startEvent' | 'endEvent'): void {
   const {
     name,
     durationMs,
-    data,
     options,
   } = event;
 
   const logTimeStamp = new Date().toLocaleString();
-  const dataString = data ? ': ' + JSON.stringify(data) : '';
+  const dataString = formatData(event);
   const {telemetric, silent} = options;
 
   switch (phase) {
@@ -94,15 +91,15 @@ function logEvent(id: number, phase: 'startEvent' | 'endEvent'): void {
       if (!silent) {
         // eslint-disable-next-line no-console-disallow
         console.log(
-          chalk.dim(`[${logTimeStamp}] <END>   ${name}${dataString} `) +
-          (telemetric ? chalk.reset.cyan(`(${+durationMs}ms)`) : chalk.dim(`(${+durationMs}ms)`))
+          chalk.dim(`[${logTimeStamp}] <END>   ${name}${dataString}`) +
+          (telemetric ? chalk.reset.cyan(` (${+durationMs}ms)`) : chalk.dim(` (${+durationMs}ms)`))
         );
       }
       forgetEvent(id);
       break;
 
     default:
-      throw new Error('Unexpected scheduled event type: ' + name);
+      throw new Error(`Unexpected event phase "${phase}"!`);
   }
 }
 
diff --git a/react-packager/src/Activity/normaliseEventData.js b/react-packager/src/Activity/normaliseEventData.js
new file mode 100644
index 00000000..df0da238
--- /dev/null
+++ b/react-packager/src/Activity/normaliseEventData.js
@@ -0,0 +1,41 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ *
+ */
+'use strict';
+
+import type {EventData, NormalisedEventData} from './Types';
+
+function normaliseEventData(eventData: EventData): NormalisedEventData {
+  if (!eventData) {
+    return {};
+  }
+
+  const normalisedEventData = {};
+
+  Object.keys(eventData).forEach(field => {
+    const value = eventData[field];
+    let type;
+
+    if (typeof value === 'string' || typeof value === 'boolean') {
+      type = 'normal';
+    } else if (typeof value === 'number') {
+      type = 'int';
+    } else {
+      throw new Error(`Disallowed value for event field "${field}""!`);
+    }
+
+    normalisedEventData[field] = {type, value};
+  });
+
+  return normalisedEventData;
+}
+
+module.exports = normaliseEventData;
diff --git a/react-packager/src/Bundler/index.js b/react-packager/src/Bundler/index.js
index f6ed1ed1..d1c2dbc6 100644
--- a/react-packager/src/Bundler/index.js
+++ b/react-packager/src/Bundler/index.js
@@ -366,11 +366,12 @@ class Bundler {
   }) {
     const findEventId = Activity.startEvent(
       'Transforming modules',
-      null,
+      {
+        entry_point: entryFile,
+        environment: dev ? 'dev' : 'prod',
+      },
       {
         telemetric: true,
-        entryPoint: entryFile,
-        details: dev ? 'dev' : 'prod',
       },
     );
     const modulesByName = Object.create(null);
diff --git a/react-packager/src/JSTransformer/index.js b/react-packager/src/JSTransformer/index.js
index 9a5619e5..e3f64e5a 100644
--- a/react-packager/src/JSTransformer/index.js
+++ b/react-packager/src/JSTransformer/index.js
@@ -114,7 +114,9 @@ class Transformer {
     debug('transforming file', fileName);
     const transformEventId = Activity.startEvent(
       'Transforming file',
-      fileName,
+      {
+        file_name: fileName,
+      },
       {
         telemetric: true,
         silent: true,
diff --git a/react-packager/src/Server/index.js b/react-packager/src/Server/index.js
index a9153d27..3778289e 100644
--- a/react-packager/src/Server/index.js
+++ b/react-packager/src/Server/index.js
@@ -499,7 +499,15 @@ class Server {
   _processAssetsRequest(req, res) {
     const urlObj = url.parse(decodeURI(req.url), true);
     const assetPath = urlObj.pathname.match(/^\/assets\/(.+)$/);
-    const assetEvent = Activity.startEvent('Processing asset request', {asset: assetPath[1]});
+    const assetEvent = Activity.startEvent(
+      'Processing asset request',
+      {
+        asset: assetPath[1],
+      },
+      {
+        displayFields: true,
+      },
+    );
     this._assetServer.get(assetPath[1], urlObj.query.platform)
       .then(
         data => {
@@ -538,10 +546,11 @@ class Server {
             Activity.startEvent(
               'Updating existing bundle',
               {
-                outdatedModules: outdated.size,
+                outdated_modules: outdated.size,
               },
               {
                 telemetric: true,
+                displayFields: true,
               },
             );
           debug('Attempt to update existing bundle');
@@ -650,11 +659,11 @@ class Server {
       'Requesting bundle',
       {
         url: req.url,
+        entry_point: options.entryFile,
       },
       {
         telemetric: true,
-        entryPoint: options.entryFile,
-        details: req.url,
+        displayFields: ['url'],
       },
     );