diff --git a/src/util/taskReporter.js b/src/util/taskReporter.js
new file mode 100644
index 0000000..ebeaa04
--- /dev/null
+++ b/src/util/taskReporter.js
@@ -0,0 +1,87 @@
+// @flow
+
+const chalk = require("chalk");
+
+type TaskId = string;
+
+type MsSinceEpoch = number;
+type ConsoleLog = (string) => void;
+type GetTime = () => MsSinceEpoch;
+
+/**
+ * This class is a lightweight utility for reporting task progress to the
+ * command line.
+ *
+ * - When a task is started, it's printed to the CLI with a " GO " label.
+ * - When it's finished, it's printed with a "DONE" label, along with the time
+ * elapsed.
+ * - Tasks are tracked and represented by string id.
+ * - The same task id may be re-used after the first task with that id is
+ * finished.
+ */
+export class TaskReporter {
+  // Maps the task to the time
+  activeTasks: Map<TaskId, MsSinceEpoch>;
+  _consoleLog: ConsoleLog;
+  _getTime: GetTime;
+
+  constructor(consoleLog?: ConsoleLog, getTime?: GetTime) {
+    this._consoleLog = consoleLog || console.log;
+    this._getTime =
+      getTime ||
+      function() {
+        return +new Date();
+      };
+    this.activeTasks = new Map();
+  }
+
+  start(taskId: TaskId) {
+    if (this.activeTasks.has(taskId)) {
+      throw new Error(`task ${taskId} already registered`);
+    }
+    this.activeTasks.set(taskId, this._getTime());
+    this._consoleLog(startMessage(taskId));
+    return this;
+  }
+
+  finish(taskId: TaskId) {
+    const startTime = this.activeTasks.get(taskId);
+    if (startTime == null) {
+      throw new Error(`task ${taskId} not registered`);
+    }
+    const elapsedTime = this._getTime() - startTime;
+    this._consoleLog(finishMessage(taskId, elapsedTime));
+    this.activeTasks.delete(taskId);
+    return this;
+  }
+}
+
+export function formatTimeElapsed(elapsed: MsSinceEpoch): string {
+  if (elapsed < 0) {
+    throw new Error("nonegative time expected");
+  }
+  if (elapsed < 1000) {
+    return `${elapsed}ms`;
+  }
+  const seconds = Math.round(elapsed / 1000);
+  const minutes = Math.floor(seconds / 60);
+  if (minutes == 0) return `${seconds}s`;
+  const hours = Math.floor(minutes / 60);
+  if (hours == 0) return `${minutes}m ${seconds % 60}s`;
+  const days = Math.floor(hours / 24);
+  if (days == 0) return `${hours}h ${minutes % 60}m`;
+  return `${days}d ${hours % 24}h`;
+}
+
+export function startMessage(taskId: string): string {
+  const label = chalk.bgBlue.bold.white("  GO  ");
+  const message = `${label} ${taskId}`;
+  return message;
+}
+
+export function finishMessage(taskId: string, elapsedTimeMs: number): string {
+  const elapsed = formatTimeElapsed(elapsedTimeMs);
+  const label = chalk.bgGreen.bold.white(" DONE ");
+  const message = `${label} ${taskId}: ${elapsed}`;
+  return message;
+}
diff --git a/src/util/taskReporter.test.js b/src/util/taskReporter.test.js
new file mode 100644
index 0000000..4893742
--- /dev/null
+++ b/src/util/taskReporter.test.js
@@ -0,0 +1,114 @@
+// @flow
+
+import {
+  TaskReporter,
+  formatTimeElapsed,
+  startMessage,
+  finishMessage,
+} from "./taskReporter";
+
+describe("util/taskReporter", () => {
+  describe("formatTimeElapsed", () => {
+    function tc(expected, ms) {
+      it(`works for ${expected}`, () => {
+        expect(formatTimeElapsed(ms)).toEqual(expected);
+      });
+    }
+    tc("0ms", 0);
+    tc("50ms", 50);
+    tc("999ms", 999);
+    const secs = 1000;
+    tc("1s", 1 * secs + 400);
+    tc("2s", 1 * secs + 600);
+    tc("59s", 59 * secs);
+    const mins = secs * 60;
+    tc("1m 3s", mins + 3 * secs);
+    tc("59m 59s", 59 * mins + 59 * secs);
+    const hours = mins * 60;
+    tc("1h 0m", hours);
+    tc("1h 3m", hours + mins * 3);
+    tc("23h 59m", 23 * hours + 59 * mins);
+    const days = 24 * hours;
+    tc("1d 0h", days);
+    tc("555d 23h", 555 * days + 23 * hours);
+  });
+
+  describe("TaskReporter", () => {
+    class TestCase {
+      _time: number;
+      messages: string[];
+      taskReporter: TaskReporter;
+
+      constructor() {
+        this._time = 0;
+        this.messages = [];
+        const logMock = (x) => {
+          this.messages.push(x);
+        };
+        const timeMock = () => this._time;
+        this.taskReporter = new TaskReporter(logMock, timeMock);
+      }
+      start(task: string) {
+        this.taskReporter.start(task);
+        return this;
+      }
+      finish(task: string) {
+        this.taskReporter.finish(task);
+        return this;
+      }
+      time(t: number) {
+        this._time = t;
+        return this;
+      }
+    }
+
+    it("errors when finishing an unregistered task", () => {
+      const fail = () => new TestCase().finish("foo");
+      expect(fail).toThrowError("task foo not registered");
+    });
+    it("errors when starting a task twice", () => {
+      const fail = () => new TestCase().start("foo").start("foo");
+      expect(fail).toThrowError("task foo already registered");
+    });
+    it("errors when finishing a task twice", () => {
+      const fail = () =>
+        new TestCase()
+          .start("foo")
+          .finish("foo")
+          .finish("foo");
+      expect(fail).toThrowError("task foo not registered");
+    });
+
+    it("works for a task that immediately finishes", () => {
+      const {messages} = new TestCase().start("foo").finish("foo");
+      expect(messages).toEqual([startMessage("foo"), finishMessage("foo", 0)]);
+    });
+
+    it("works when two tasks are started, then one finishes", () => {
+      const {messages} = new TestCase()
+        .start("foo")
+        .start("bar")
+        .time(200)
+        .finish("foo");
+      expect(messages).toEqual([
+        startMessage("foo"),
+        startMessage("bar"),
+        finishMessage("foo", 200),
+      ]);
+    });
+    it("works when a task is started, finished, and re-started", () => {
+      const {messages} = new TestCase()
+        .start("foo")
+        .finish("foo")
+        .start("foo")
+        .time(200)
+        .finish("foo");
+      expect(messages).toEqual([
+        startMessage("foo"),
+        finishMessage("foo", 0),
+        startMessage("foo"),
+        finishMessage("foo", 200),
+      ]);
+    });
+  });
+});