diff --git a/README.md b/README.md
index 1e514db..c56ce3c 100644
--- a/README.md
+++ b/README.md
@@ -37,7 +37,9 @@ module.exports = {
     yarn: '~1.17.3',
     nginx: {
       semver: '>= 1.16.x',
-      optional: true // optional (won't fail)
+      optional: true, // optional (won't fail)
+      installMessage: '<install instruction>', // custom message when binary is not found
+      updateMessage: '<update instruction>' // custom message when binary has wrong version
     },
     httpd: {
       semver: '^1.x',
@@ -58,7 +60,7 @@ $ npx requirements
 Or use a custom path:
 
 ```bash
-$ npx requirements --config=<filepath>
+$ npx requirements --config <filepath>
 ```
 
 # CLI options
@@ -105,8 +107,19 @@ checkSoftware() returns an Array with results
 ];
 ```
 
+# testing
+
+```bash
+# test functionality
+yarn build
+node bin/requirements.js --config tests/requirements.config.js
+
+# unit tests
+yarn test
+```
+
 # license
 
 The MIT License (MIT)
 
-Copyright (c) 2017-2019 Steven Chim
+Copyright (c) 2017-2020 Steven Chim
diff --git a/src/__tests__/results.spec.ts b/src/__tests__/results.spec.ts
new file mode 100644
index 0000000..5c730db
--- /dev/null
+++ b/src/__tests__/results.spec.ts
@@ -0,0 +1,52 @@
+import * as fs from 'fs';
+import { isAllOK, getMessages } from '../results';
+import { RawResult } from '../types';
+
+describe('results', () => {
+  describe('all results OK', () => {
+    it('should indicate all results are OK', async () => {
+      const rawResults: RawResult[] = [
+        {
+          bin: 'mvn',
+          satisfies: true
+        } as RawResult
+      ];
+
+      const result = isAllOK(rawResults);
+      expect(result).toBe(true);
+    });
+
+    it('should indicate all results are OK', async () => {
+      const rawResults: RawResult[] = [
+        {
+          bin: 'mvn',
+          satisfies: false
+        } as RawResult
+      ];
+
+      const result = isAllOK(rawResults);
+      expect(result).toBe(false);
+    });
+  });
+
+  describe('custom messages', () => {
+    it('should return messages', async () => {
+      const rawResults: RawResult[] = [
+        {
+          bin: 'mvn',
+          installed: false,
+          installMessage: '<mvn install instructions>'
+        } as RawResult,
+        {
+          bin: 'nginx',
+          satisfies: false,
+          updateMessage: '<nginx update instructions>'
+        } as RawResult
+      ];
+
+      const result = getMessages(rawResults);
+      const expectation = ['<mvn install instructions>', '<nginx update instructions>'];
+      expect(result).toEqual(expectation);
+    });
+  });
+});
diff --git a/src/bin.ts b/src/bin.ts
index a0165b2..880732b 100644
--- a/src/bin.ts
+++ b/src/bin.ts
@@ -2,9 +2,10 @@ import * as yargs from 'yargs';
 import * as path from 'path';
 import * as chalk from 'chalk';
 import { checkSoftware } from './requirements';
-import { renderTable } from './reporter';
+import { renderTable, renderMessages } from './reporter';
 import { Configuration } from './types';
 import { scaffold } from './scaffold';
+import { isAllOK, getMessages } from './results';
 
 export async function exec(_debug_argv_?) {
   const argv = _debug_argv_ ?? getArgv();
@@ -21,9 +22,7 @@ export async function exec(_debug_argv_?) {
   const config = getConfiguration(argv);
   let rawResults = await checkSoftware(config.software);
 
-  const ALL_OK = rawResults
-    .filter(result => !result.optional)
-    .every(result => result.satisfies === true);
+  const ALL_OK = isAllOK(rawResults);
 
   if (argv.debug) {
     console.debug('👀  RAW data:\n', rawResults);
@@ -31,7 +30,9 @@ export async function exec(_debug_argv_?) {
   }
 
   if (!ALL_OK && !argv.force) {
+    const messages = getMessages(rawResults);
     console.error(renderTable(rawResults));
+    console.log(renderMessages(messages));
     throw new Error(`❌  Not all requirements are satisfied`);
   }
 
diff --git a/src/reporter.ts b/src/reporter.ts
index 00da46a..ceb4f32 100644
--- a/src/reporter.ts
+++ b/src/reporter.ts
@@ -3,6 +3,10 @@ import * as logSymbols from 'log-symbols';
 import * as chalk from 'chalk';
 import { RawResult } from './types';
 
+export function renderMessages(messages: string[] = []) {
+  return messages.map(message => `${chalk.red('❗️')}  ${message}`).join('\n') + '\n';
+}
+
 export function renderTable(rawResults: RawResult[] = []) {
   let results = rawResults.map(item => {
     const { bin, semver, installed, version, satisfies, optional } = item;
diff --git a/src/results.ts b/src/results.ts
new file mode 100644
index 0000000..2dccd07
--- /dev/null
+++ b/src/results.ts
@@ -0,0 +1,18 @@
+import { RawResult } from './types';
+
+export function isAllOK(rawResults: RawResult[]) {
+  return rawResults.filter(result => !result.optional).every(result => result.satisfies === true);
+}
+
+export function getMessages(rawResults: RawResult[]) {
+  const notInstalledItems = rawResults.filter(item => !item.installed && item.installMessage);
+  const unsatisfiedInstalledItems = rawResults.filter(
+    item => !item.satisfies && item.updateMessage
+  );
+
+  const messages = [...notInstalledItems, ...unsatisfiedInstalledItems].map(item => {
+    return item.installMessage || item.updateMessage;
+  });
+
+  return messages;
+}
diff --git a/src/scaffold.ts b/src/scaffold.ts
index 2ab1f3f..e0f3eab 100644
--- a/src/scaffold.ts
+++ b/src/scaffold.ts
@@ -9,11 +9,13 @@ const TEMPLATE = `module.exports = {
     node: '^${semver.clean(process.version)}',
     nginx: {
       semver: '^666.x',
-      optional: true      // won't fail if missing or wrong version
+      optional: true       // won't fail if missing or wrong version
     },
     // httpd: {
     //   semver: '^2.x',
-    //   flag: '-v'       // custom flag to print version
+    //   flag: '-v',       // custom flag to print version
+    //   installMessage: '<install instruction>',     // custom message when binary is not found
+    //   updateMessage: '<update instruction>',       // custom message when binary has wrong version
     // },
   }
 };`;
diff --git a/src/types.ts b/src/types.ts
index 17d75cd..4169238 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -10,18 +10,17 @@ export type ConfigurationValue = ConfigurationStringValue | ConfigurationObjectV
 
 export type ConfigurationStringValue = string;
 
-export type ConfigurationObjectValue = {
+export interface ConfigurationObjectValue {
   semver: string;
   flag: string;
   optional?: boolean;
-};
+  installMessage?: string;
+  updateMessage?: string;
+}
 
-export interface RawResult {
+export interface RawResult extends ConfigurationObjectValue {
   bin: string;
-  semver: string;
-  flag: string;
   installed: boolean;
   version?: string;
   satisfies?: boolean;
-  optional?: boolean;
 }
diff --git a/tests/requirements.config.js b/tests/requirements.config.js
index 5f381dc..1600dfb 100644
--- a/tests/requirements.config.js
+++ b/tests/requirements.config.js
@@ -4,11 +4,15 @@ module.exports = {
     git: '~1.9.4 || 2.0.0 - 2.10.0',
     node: '8 || 10 || 12',
     npm: '>= 6.x',
-    yarn: '>= 1.19.x',
+    yarn: {
+      semver: '1.16.x',
+      updateMessage: `Outdated 'yarn' found. Run 'brew upgrade yarn' to update.`
+    },
     mvn: '^3.x',
     nginx: {
       semver: '^6.x',
-      optional: true
+      optional: true,
+      installMessage: `This project is configured for NGINX but 'nginx' was not found on your path. Run 'brew install nginx' to install.`
     },
     httpd: {
       semver: '^2.x',