diff --git a/README.md b/README.md
index bd4af51e..7ba3473a 100644
--- a/README.md
+++ b/README.md
@@ -88,6 +88,11 @@ tcm -p 'src/**/*.icss' .
 
 With `-w` or `--watch`, this CLI watches files in the input directory.
 
+#### validating type files
+
+With `-l` or `--listDifferent`, list any files that are different than those that would be generated.
+If any are different, exit with a status code 1.
+
 #### camelize CSS token
 
 With `-c` or `--camelCase`, kebab-cased CSS classes(such as `.my-class {...}`) are exported as camelized TypeScript varibale name(`export const myClass: string`).
diff --git a/src/cli.ts b/src/cli.ts
index 31896b99..5e4ffa72 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -16,6 +16,12 @@ const yarg = yargs
   .alias('o', 'outDir')
   .describe('o', 'Output directory')
   .string('o')
+  .alias('l', 'listDifferent')
+  .describe(
+    'l',
+    'List any files that are different than those that would be generated. If any are different, exit with a status code 1.',
+  )
+  .boolean('l')
   .alias('w', 'watch')
   .describe('w', "Watch input directory's css files or pattern")
   .boolean('w')
@@ -63,5 +69,6 @@ async function main(): Promise<void> {
     namedExports: argv.e,
     dropExtension: argv.d,
     silent: argv.s,
+    listDifferent: argv.l,
   });
 }
diff --git a/src/dts-content.ts b/src/dts-content.ts
index 81e02416..98fd0cd4 100644
--- a/src/dts-content.ts
+++ b/src/dts-content.ts
@@ -5,6 +5,7 @@ import isThere from 'is-there';
 import * as mkdirp from 'mkdirp';
 import * as util from 'util';
 import camelcase from 'camelcase';
+import chalk from 'chalk';
 
 const writeFile = util.promisify(fs.writeFile);
 const readFile = util.promisify(fs.readFile);
@@ -90,6 +91,26 @@ export class DtsContent {
     return path.join(this.rootDir, this.searchDir, this.rInputPath);
   }
 
+  public get relativeInputFilePath(): string {
+    return path.join(this.searchDir, this.rInputPath);
+  }
+
+  public async checkFile(postprocessor = (formatted: string) => formatted): Promise<boolean> {
+    if (!isThere(this.outputFilePath)) {
+      console.error(chalk.red(`[ERROR] Type file needs to be generated for '${this.relativeInputFilePath}'`));
+      return false;
+    }
+
+    const finalOutput = postprocessor(this.formatted);
+    const fileContent = (await readFile(this.outputFilePath)).toString();
+
+    if (fileContent !== finalOutput) {
+      console.error(chalk.red(`[ERROR] Check type definitions for '${this.outputFilePath}'`));
+      return false;
+    }
+    return true;
+  }
+
   public async writeFile(postprocessor = (formatted: string) => formatted): Promise<void> {
     const finalOutput = postprocessor(this.formatted);
 
diff --git a/src/run.ts b/src/run.ts
index 8ac660fd..8c17d8f0 100644
--- a/src/run.ts
+++ b/src/run.ts
@@ -16,6 +16,7 @@ interface RunOptions {
   namedExports?: boolean;
   dropExtension?: boolean;
   silent?: boolean;
+  listDifferent?: boolean;
 }
 
 export async function run(searchDir: string, options: RunOptions = {}): Promise<void> {
@@ -30,6 +31,16 @@ export async function run(searchDir: string, options: RunOptions = {}): Promise<
     dropExtension: options.dropExtension,
   });
 
+  const checkFile = async (f: string): Promise<boolean> => {
+    try {
+      const content: DtsContent = await creator.create(f, undefined, false);
+      return await content.checkFile();
+    } catch (error) {
+      console.error(chalk.red(`[ERROR] An error occurred checking '${f}':\n${error}`));
+      return false;
+    }
+  };
+
   const writeFile = async (f: string): Promise<void> => {
     try {
       const content: DtsContent = await creator.create(f, undefined, !!options.watch);
@@ -43,6 +54,15 @@ export async function run(searchDir: string, options: RunOptions = {}): Promise<
     }
   };
 
+  if (options.listDifferent) {
+    const files = await glob(filesPattern);
+    const hasErrors = (await Promise.all(files.map(checkFile))).includes(false);
+    if (hasErrors) {
+      process.exit(1);
+    }
+    return;
+  }
+
   if (!options.watch) {
     const files = await glob(filesPattern);
     await Promise.all(files.map(writeFile));
diff --git a/test/different.css b/test/different.css
new file mode 100644
index 00000000..9a768bac
--- /dev/null
+++ b/test/different.css
@@ -0,0 +1 @@
+.myClass {color: red;}
diff --git a/test/different.css.d.ts b/test/different.css.d.ts
new file mode 100644
index 00000000..e31e5041
--- /dev/null
+++ b/test/different.css.d.ts
@@ -0,0 +1,4 @@
+declare const styles: {
+  readonly "differentClass": string;
+};
+export = styles;
diff --git a/test/dts-creator.spec.ts b/test/dts-creator.spec.ts
index 6cf0358d..fc896900 100644
--- a/test/dts-creator.spec.ts
+++ b/test/dts-creator.spec.ts
@@ -3,8 +3,8 @@
 import * as path from 'path';
 
 import * as assert from 'assert';
-import * as os from 'os';
 import { DtsCreator } from '../src/dts-creator';
+import SpyInstance = jest.SpyInstance;
 
 describe('DtsCreator', () => {
   var creator = new DtsCreator();
@@ -91,6 +91,15 @@ describe('DtsContent', () => {
     });
   });
 
+  describe('#relativeInputFilePath', () => {
+    it('returns relative original CSS file name', done => {
+      new DtsCreator().create(path.normalize('test/testStyle.css')).then(content => {
+        assert.equal(content.relativeInputFilePath, 'test/testStyle.css');
+        done();
+      });
+    });
+  });
+
   describe('#outputFilePath', () => {
     it('adds d.ts to the original filename', done => {
       new DtsCreator().create(path.normalize('test/testStyle.css')).then(content => {
@@ -210,6 +219,66 @@ export = styles;
     });
   });
 
+  describe('#checkFile', () => {
+    let mockExit: SpyInstance;
+    let mockConsoleLog: SpyInstance;
+    let mockConsoleError: SpyInstance;
+
+    beforeAll(() => {
+      mockExit = jest.spyOn(process, 'exit').mockImplementation(exitCode => {
+        throw new Error(`process.exit: ${exitCode}`);
+      });
+      mockConsoleLog = jest.spyOn(console, 'log').mockImplementation();
+      mockConsoleError = jest.spyOn(console, 'error').mockImplementation();
+    });
+
+    beforeEach(() => {
+      jest.clearAllMocks();
+    });
+
+    afterAll(() => {
+      mockExit.mockRestore();
+      mockConsoleLog.mockRestore();
+      mockConsoleError.mockRestore();
+    });
+
+    it('return false if type file is missing', done => {
+      new DtsCreator()
+        .create('test/empty.css')
+        .then(content => {
+          return content.checkFile();
+        })
+        .then(result => {
+          assert.equal(result, false);
+          done();
+        });
+    });
+
+    it('returns false if type file content is different', done => {
+      new DtsCreator()
+        .create('test/different.css')
+        .then(content => {
+          return content.checkFile();
+        })
+        .then(result => {
+          assert.equal(result, false);
+          done();
+        });
+    });
+
+    it('returns true if type files match', done => {
+      new DtsCreator()
+        .create('test/testStyle.css')
+        .then(content => {
+          return content.checkFile();
+        })
+        .then(result => {
+          assert.equal(result, true);
+          done();
+        });
+    });
+  });
+
   describe('#writeFile', () => {
     it('accepts a postprocessor function', done => {
       new DtsCreator()