diff --git a/README.md b/README.md
index dde35ea..e6cdc24 100755
--- a/README.md
+++ b/README.md
@@ -17,6 +17,7 @@ Read and explore NetCDF files
 ## Example
 
 ```js
+const fs = require('fs');
 const netcdfjs = require('netcdfjs');
 ```
 
diff --git a/package.json b/package.json
index 693c949..c26a613 100755
--- a/package.json
+++ b/package.json
@@ -34,5 +34,8 @@
     "mocha": "^3.1.2",
     "mocha-better-spec-reporter": "^3.0.2",
     "should": "^11.1.1"
+  },
+  "dependencies": {
+    "iobuffer": "^2.1.0"
   }
 }
diff --git a/src/index.js b/src/index.js
index 8076ae0..8998162 100755
--- a/src/index.js
+++ b/src/index.js
@@ -1,7 +1,30 @@
 'use strict';
 
-module.exports = netcdf;
+const IOBuffer = require('iobuffer');
 
-function netcdf() {
-    return true;
+function netcdf(data) {
+    const buffer = new IOBuffer(data);
+
+    // Validate that it's a NetCDF file
+    notNetcdf((buffer.readChars(3) !== 'CDF'), 'should start with CDF');
+
+    // Check the NetCDF format
+    const version = buffer.readByte();
+    notNetcdf((version === 2), '64-bit offset format not supported yet');
+    notNetcdf((version !== 1), 'unknown version');
+
+    return buffer.length;
 }
+
+/**
+ * Throws a non-valid NetCDF exception if the statement it's true
+ * @param {boolean} statement - Throws if true
+ * @param {string} reason - Reason to throw
+ */
+function notNetcdf(statement, reason) {
+    if (statement) {
+        throw new TypeError('Not a valid NetCDF v3.x file: ' + reason);
+    }
+}
+
+module.exports = netcdf;
diff --git a/test/files/madis-sao.nc b/test/files/madis-sao.nc
new file mode 100644
index 0000000..3360f77
Binary files /dev/null and b/test/files/madis-sao.nc differ
diff --git a/test/files/not_nc.txt b/test/files/not_nc.txt
new file mode 100644
index 0000000..0b8d5e1
--- /dev/null
+++ b/test/files/not_nc.txt
@@ -0,0 +1 @@
+This is not a NetCDF file
\ No newline at end of file
diff --git a/test/files/test_hgroups.nc b/test/files/test_hgroups.nc
new file mode 100644
index 0000000..d688c4c
Binary files /dev/null and b/test/files/test_hgroups.nc differ
diff --git a/test/test.js b/test/test.js
index cc11652..96677f4 100755
--- a/test/test.js
+++ b/test/test.js
@@ -1,9 +1,19 @@
 'use strict';
 
 const netcdfjs = require('..');
+const fs = require('fs');
+const pathFiles = __dirname + '/files/';
 
-describe('test', function () {
-    it('should be tested', function () {
-        (42).should.equal(42);
+describe('Read file', function () {
+    it('Throws on non NetCDF file', function () {
+        const data = fs.readFileSync(pathFiles + 'not_nc.txt');
+        netcdfjs.bind(null, data).should.throw('Not a valid NetCDF v3.x file: should start with CDF');
+    });
+
+    it('read header information', function () {
+        // http://www.unidata.ucar.edu/software/netcdf/examples/files.html
+        const data = fs.readFileSync(pathFiles + 'madis-sao.nc');
+
+        netcdfjs(data).should.be.equal(266032);
     });
 });
diff --git a/yarn.lock b/yarn.lock
index 97ad11b..e7f3d7c 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3096,6 +3096,10 @@ invert-kv@^1.0.0:
   version "1.0.0"
   resolved "https://registry.yarnpkg.com/invert-kv/-/invert-kv-1.0.0.tgz#104a8e4aaca6d3d8cd157a8ef8bfab2d7a3ffdb6"
 
+iobuffer:
+  version "2.1.0"
+  resolved "https://registry.yarnpkg.com/iobuffer/-/iobuffer-2.1.0.tgz#074882d24020a85db6a5042a0418ef9b6b2e616a"
+
 irregular-plurals@^1.0.0:
   version "1.2.0"
   resolved "https://registry.yarnpkg.com/irregular-plurals/-/irregular-plurals-1.2.0.tgz#38f299834ba8c00c30be9c554e137269752ff3ac"