diff --git a/README.md b/README.md
index aeda1d5..18458de 100644
--- a/README.md
+++ b/README.md
@@ -1,19 +1,18 @@
 [![Docker Automated build](https://img.shields.io/docker/automated/clapclapexcitement/concourse-consul-kv-resource.svg?style=flat)](https://hub.docker.com/r/clapclapexcitement/concourse-consul-kv-resource/)
 [![Build Status](https://travis-ci.org/mdb/concourse-consul-kv-resource.svg?branch=master)](https://travis-ci.org/mdb/concourse-consul-kv-resource)
 
-
 # concourse-consul-kv-resource
 
 A [Concourse](http://concourse.ci/) resource for interacting with [Consul's KV store](https://www.consul.io/api/kv.html).
 
-`concourse-consul-kv-resource` can be used to get or set a key in Consul's KV store.
+`concourse-consul-kv-resource` can be used to get or set a key/value in Consul's KV store.
 
 ## Source configuration
 
 * `key`: _Required_. The Consul key to interact with. Note that all URL path parts following `/v1/kv` are required. For example, if your key is `my-consul:8500/v1/kv/my/key`, then `key` should be "my/key".
 * `host`: _Required_. The Consul host.
-* `token`: _Required_. A Consul ACL token.
-* `tls_cert`: _Required_. A TLS cert for the Consul.
+* `token`: _Optional_. A Consul ACL token.
+* `tls_cert`: _Optional_. A TLS cert for the Consul.
 * `tls_key`: _Required_. A TLS cert key for the Consul.
 * `port`: _Optional_. The port on which the Consul API is hosted. Defaults to `8500`.
 * `protocol`: _Optional_. The protocol to use in calling the Consul API. Defaults to `https`.
@@ -23,7 +22,30 @@ A [Concourse](http://concourse.ci/) resource for interacting with [Consul's KV s
 
 ### `in`: Get a Consul KV key's value
 
-Gets the value of the Consul KV key configured in the source.
+Gets the value of the Consul KV key configured in the source. The key's plain text value is written to a `<resource-get>/<key-name>` file.
+
+For example, the following pipeline's `get-my-consul-key` job writes the `foo` key's value to a `my-consul-key/my/key` file:
+
+```yaml
+...
+
+resources:
+
+- name: my-consul-key
+  type: consul-kv
+  source:
+    token: my-acl-token
+    host: my-consul.com
+    tls_cert: my-cert-string
+    tls_key: my-cert-key-string
+    key: my/key
+
+jobs:
+
+- name: get-my-consul-key
+  plan:
+  - get: my-consul-key
+```
 
 ### `out`: Set a Consul KV key's value
 
@@ -38,7 +60,7 @@ Sets the Consul KV key configured in the source to the value specified in the pa
 
 ## Example pipeline
 
-```
+```yaml
 resources:
 
 - name: my-consul-key
@@ -60,6 +82,10 @@ resource_types:
 
 jobs:
 
+- name: get-my-consul-key
+  plan:
+  - get: my-consul-key
+
 - name: set-my-consul-key
   plan:
   - put: my-consul-key
diff --git a/assets/check.js b/assets/check.js
index 7acedda..64d0062 100644
--- a/assets/check.js
+++ b/assets/check.js
@@ -1,11 +1,12 @@
 #!/usr/bin/env node
 
-'use strict';
-
 const checkAction = require('./lib/check');
 const handlers = require('./lib/handlers');
 
 checkAction()
-  .then((result) => {
+  .then(result => {
     handlers.success(result);
+  })
+  .catch(problem => {
+    handlers.fail(problem);
   });
diff --git a/assets/in.js b/assets/in.js
index e1858a9..dfc38d5 100644
--- a/assets/in.js
+++ b/assets/in.js
@@ -1,11 +1,12 @@
 #!/usr/bin/env node
 
-'use strict';
-
 const inAction = require('./lib/in');
 const handlers = require('./lib/handlers');
 
 inAction(process.argv[2])
   .then(result => {
     handlers.success(result);
+  })
+  .catch(problem => {
+    handlers.fail(problem);
   });
diff --git a/assets/lib/check.js b/assets/lib/check.js
index 0547515..2925b5d 100644
--- a/assets/lib/check.js
+++ b/assets/lib/check.js
@@ -1,22 +1,32 @@
-'use strict';
-
 const Client = require('./client');
-const handlers = require('./handlers');
 
 function checkAction() {
-  return new Promise(resolve => {
+  return new Promise((resolve, reject) => {
     process.stdin.on('data', stdin => {
-      let data = JSON.parse(stdin);
-      let source = data.source || {};
-      let client = new Client(source);
+      const data = JSON.parse(stdin);
+      const source = data.source || {};
+      const client = new Client(source);
+      const previousVersion = data.version && data.version.value ? data.version.value : undefined;
 
       client.get(source.key)
         .then(value => {
-          resolve([{
-            value: value.value
-          }]);
+          if (!value.value) {
+            reject(new Error(`${source.key} has no value`));
+
+            return;
+          }
+
+          if (!previousVersion || previousVersion !== value.value) {
+            resolve([{
+              value: value.value
+            }]);
+
+            return;
+          }
+
+          resolve([]);
         }, rejected => {
-          handlers.fail(rejected);
+          reject(rejected);
         });
     });
   });
diff --git a/assets/lib/client.js b/assets/lib/client.js
index d1d6749..162af68 100644
--- a/assets/lib/client.js
+++ b/assets/lib/client.js
@@ -1,5 +1,3 @@
-'use strict';
-
 const Consul = require('consul-kv');
 
 class Client {
diff --git a/assets/lib/handlers.js b/assets/lib/handlers.js
index 032e031..f915332 100644
--- a/assets/lib/handlers.js
+++ b/assets/lib/handlers.js
@@ -1,5 +1,3 @@
-'use strict';
-
 module.exports = {
   fail: function(err) {
     if (err) {
diff --git a/assets/lib/in.js b/assets/lib/in.js
index 408d10e..63ca0d1 100644
--- a/assets/lib/in.js
+++ b/assets/lib/in.js
@@ -1,35 +1,42 @@
-'use strict';
-
 const fs = require('fs-extra');
 const Client = require('./client');
-const handlers = require('./handlers');
 
 function inAction(destDir) {
-  return new Promise(resolve => {
+  return new Promise((resolve, reject) => {
     process.stdin.on('data', stdin => {
-      let data = JSON.parse(stdin);
-      let source = data.source || {};
-      let client = new Client(source);
-      let file = `${destDir}/${source.key}`;
+      const data = JSON.parse(stdin);
+      const source = data.source || {};
+      const client = new Client(source);
+      const file = `${destDir}/${source.key}`;
 
       client.get(source.key).then(value => {
-        fs.ensureFile(file, (err) => {
-          if (err) handlers.fail(err);
+        fs.ensureFile(file, err => {
+          if (err) {
+            reject(err);
+
+            return;
+          }
+
+          fs.writeFile(file, value.value, err => {
+            if (err) {
+              reject(err);
 
-          fs.writeFile(file, value.value, (err) => {
-            if (err) handlers.fail(err);
+              return;
+            }
 
             resolve({
               version: {
-                value: value.value,
-                // timestamp in milliseconds:
-                ref: Date.now().toString()
-              }
+                value: value.value
+              },
+              metadata: [{
+                name: 'value',
+                value: value.value
+              }]
             });
           });
         });
       }, rejected => {
-        handlers.fail(rejected);
+        reject(rejected);
       });
     });
   });
diff --git a/assets/lib/out.js b/assets/lib/out.js
index e74b130..9153571 100644
--- a/assets/lib/out.js
+++ b/assets/lib/out.js
@@ -1,48 +1,54 @@
-'use strict';
-
 const Client = require('./client');
-const handlers = require('./handlers');
 const fs = require('fs');
 
 function getValue(params, sourceDir) {
-  return new Promise(resolve => {
+  return new Promise((resolve, reject) => {
     if (params.value && params.file) {
-      handlers.fail(new Error('Both `file` and `value` present in params'));
+      reject(new Error('Both `file` and `value` present in params'));
     }
 
     if (params.file) {
       fs.readFile(`${sourceDir}/${params.file}`, (err, val) => {
-        if (err) handlers.fail(err);
+        if (err) {
+          reject(err);
+
+          return;
+        }
 
         resolve(val.toString().replace(/\n$/, ''));
       });
-    } else {
-      resolve(params.value);
+
+      return;
     }
+
+    resolve(params.value);
   });
 }
 
 function outAction(sourceDir) {
-  return new Promise(resolve => {
+  return new Promise((resolve, reject) => {
     process.stdin.on('data', stdin => {
-      let data = JSON.parse(stdin);
-      let source = data.source || {};
-      let client = new Client(source);
+      const data = JSON.parse(stdin);
+      const source = data.source || {};
+      const client = new Client(source);
 
       getValue(data.params, sourceDir).then(value => {
         client.set(source.key, value).then(() => {
           resolve({
             version: {
-              // timestamp in milliseconds:
-              ref: Date.now().toString()
+              value: value
             },
             metadata: [{
+              name: 'timestamp',
+              // timestamp in milliseconds:
+              value: Date.now().toString()
+            }, {
               name: 'value',
               value: value
             }]
           });
         }, rejected => {
-          handlers.fail(rejected);
+          reject(rejected);
         });
       });
     });
diff --git a/assets/out.js b/assets/out.js
index de15929..51d435b 100644
--- a/assets/out.js
+++ b/assets/out.js
@@ -1,11 +1,12 @@
 #!/usr/bin/env node
 
-'use strict';
-
 const outAction = require('./lib/out');
 const handlers = require('./lib/handlers');
 
 outAction(process.argv[2])
   .then(result => {
     handlers.success(result);
+  })
+  .catch(problem => {
+    handlers.fail(problem);
   });
diff --git a/package-lock.json b/package-lock.json
index 30de97c..e92a849 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "consul-kv-resource",
-  "version": "0.0.8",
+  "version": "0.9.0",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
diff --git a/package.json b/package.json
index 0765df8..b343489 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "consul-kv-resource",
-  "version": "0.0.8",
+  "version": "0.9.0",
   "description": "Get and update Consul K/V from Concourse pipelines",
   "author": "Mike Ball",
   "scripts": {
diff --git a/test/check_test.js b/test/check_test.js
index 27b5870..8440adc 100644
--- a/test/check_test.js
+++ b/test/check_test.js
@@ -1,5 +1,3 @@
-'use strict';
-
 const assert = require('assert');
 const nock = require('nock');
 const checkAction = require('../assets/lib/check');
@@ -12,6 +10,26 @@ function mockGet() {
     }]);
 }
 
+function mockGetNotFound() {
+  return nock('https://my-consul.com:8500')
+    .get('/v1/kv/my/key?token=my-token')
+    .reply(404, '');
+}
+
+function sourceJson(extra) {
+  extra = extra || {};
+
+  return JSON.stringify(Object.assign({
+    source: {
+      host: 'my-consul.com',
+      tls_cert: 'my-cert',
+      tls_key: 'my-cert-key',
+      token: 'my-token',
+      key: 'my/key'
+    }
+  }, extra));
+}
+
 describe('checkAction', () => {
   let stdin;
 
@@ -19,27 +37,80 @@ describe('checkAction', () => {
     stdin = require('mock-stdin').stdin();
   });
 
-  it('gets the Consul key configured in the source and resolves its promise with the value', () => {
-    mockGet();
-
-    process.nextTick(() => {
-      stdin.send(JSON.stringify({
-        source: {
-          host: 'my-consul.com',
-          tls_cert: 'my-cert',
-          tls_key: 'my-cert-key',
-          token: 'my-token',
-          key: 'my/key'
-        }
-      }));
+  describe('when there is no key value in Consul', () => {
+    it('rejects its promise with a meaningful message', () => {
+      mockGetNotFound();
+
+      process.nextTick(() => {
+        stdin.send(sourceJson());
+      });
+
+      return checkAction()
+        .then()
+        .catch(rejected => {
+          assert.equal(rejected.message, 'my/key has no value');
+        });
     });
+  });
+
+  describe('when there is no existing version', () => {
+    it('gets the Consul key configured in the source and resolves its promise with the value', () => {
+      mockGet();
 
-    return checkAction()
-      .then(result => {
-        assert.equal(result.length, 1);
-        assert.deepEqual(result[0], { value: 'my-value' });
-      }, rejected => {
-        console.log('rejected: ', rejected);
+      process.nextTick(() => {
+        stdin.send(sourceJson());
       });
+
+      return checkAction()
+        .then(result => {
+          assert.equal(result.length, 1);
+          assert.deepEqual(result[0], { value: 'my-value' });
+        }, rejected => {
+          console.log('rejected: ', rejected);
+        });
+    });
+  });
+
+  describe('when there is an existing version but it has the same value as the current Consul key', () => {
+    it('resolves its promise with an empty array', () => {
+      mockGet();
+
+      process.nextTick(() => {
+        stdin.send(sourceJson({
+          version: {
+            value: 'my-value'
+          }
+        }));
+      });
+
+      return checkAction()
+        .then(result => {
+          assert.equal(result.length, 0);
+        }, rejected => {
+          console.log('rejected: ', rejected);
+        });
+    });
+  });
+
+  describe('when there is an existing version and it is different from the current Consul key value', () => {
+    it('gets the Consul key configured in the source and resolves its promise with the new value', () => {
+      mockGet();
+
+      process.nextTick(() => {
+        stdin.send(sourceJson({
+          version: {
+            value: 'my-original-value'
+          }
+        }));
+      });
+
+      return checkAction()
+        .then(result => {
+          assert.equal(result.length, 1);
+          assert.deepEqual(result[0], { value: 'my-value' });
+        }, rejected => {
+          console.log('rejected: ', rejected);
+        });
+    });
   });
 });
diff --git a/test/in_test.js b/test/in_test.js
index d26b58d..677e30a 100644
--- a/test/in_test.js
+++ b/test/in_test.js
@@ -1,5 +1,3 @@
-'use strict';
-
 const assert = require('assert');
 const inAction = require('../assets/lib/in');
 const nock = require('nock');
@@ -13,36 +11,55 @@ function mockGet() {
     }]);
 }
 
+function sourceJson() {
+  return JSON.stringify({
+    source: {
+      host: 'my-consul.com',
+      tls_cert: 'my-cert',
+      tls_key: 'my-cert-key',
+      token: 'my-token',
+      key: 'my/key'
+    }
+  });
+}
+
 describe('inAction', () => {
   let stdin;
+  let result;
 
   beforeEach(() => {
     stdin = require('mock-stdin').stdin();
-  });
 
-  it('gets the Consul key configured in the source and resolves the promise with the proper metadata', () => {
     mockGet();
 
     process.nextTick(() => {
-      stdin.send(JSON.stringify({
-        source: {
-          host: 'my-consul.com',
-          tls_cert: 'my-cert',
-          tls_key: 'my-cert-key',
-          token: 'my-token',
-          key: 'my/key'
-        }
-      }));
+      stdin.send(sourceJson());
     });
 
     return inAction('test-dir')
-      .then(result => {
-        assert.equal(result.version.value, 'my-value');
+      .then(res => {
+        result = res;
       });
   });
 
-  afterEach((done) => {
-    fs.remove('test-dir', (err) => {
+  it('gets the Consul key configured in the source and resolves the promise with the proper version', () => {
+    assert.equal(result.version.value, 'my-value');
+  });
+
+  it('gets the Consul key configured in the source and resolves the promise with the proper metadata', () => {
+    assert.equal(result.metadata[0].value, 'my-value');
+  });
+
+  it('writes the Consul key configured in the source to a <key-name> file in the destination dir it is passed', () => {
+    fs.readFile('test-dir/my/key', (err, val) => {
+      if (!err) {
+        assert.equal(val, 'my-value');
+      }
+    });
+  });
+
+  afterEach(done => {
+    fs.remove('test-dir', err => {
       if (!err) done();
     });
   });
diff --git a/test/out_test.js b/test/out_test.js
index c5555e7..18e3e9c 100644
--- a/test/out_test.js
+++ b/test/out_test.js
@@ -1,5 +1,3 @@
-'use strict';
-
 const assert = require('assert');
 const outAction = require('../assets/lib/out');
 const nock = require('nock');
@@ -10,6 +8,19 @@ function mockPut(value) {
     .reply(200, 'true');
 }
 
+function sourceJson(params) {
+  return JSON.stringify({
+    source: {
+      host: 'my-consul.com',
+      tls_cert: 'my-cert',
+      tls_key: 'my-cert-key',
+      token: 'my-token',
+      key: 'my/key'
+    },
+    params: params
+  });
+}
+
 describe('outAction', () => {
   let stdin;
 
@@ -18,56 +29,66 @@ describe('outAction', () => {
   });
 
   describe('when it is passed params with a `value`', () => {
-    it('sets the Consul key to the value cited in the params.value and resolves the promise with the proper metadata', () => {
+    let result;
+
+    beforeEach(() => {
       mockPut('my-value');
 
       process.nextTick(() => {
-        stdin.send(JSON.stringify({
-          source: {
-            host: 'my-consul.com',
-            tls_cert: 'my-cert',
-            tls_key: 'my-cert-key',
-            token: 'my-token',
-            key: 'my/key'
-          },
-          params: {
-            value: 'my-value'
-          }
+        stdin.send(sourceJson({
+          value: 'my-value'
         }));
       });
 
       return outAction()
-        .then(result => {
-          assert.equal(result.metadata[0].name, 'value');
-          assert.equal(result.metadata[0].value, 'my-value');
+        .then(res => {
+          result = res;
         });
     });
+
+    it('sets the Consul key to the value cited in the params.value and resolves the promise with the proper version', () => {
+      assert.equal(result.version.value, 'my-value');
+    });
+
+    it('sets the Consul key to the value cited in the params.value and resolves the promise with metadata that includes a "timestamp"', () => {
+      assert.equal(result.metadata[0].name, 'timestamp');
+    });
+
+    it('sets the Consul key to the value cited in the params.value and resolves the promise with metadata that includes a "value"', () => {
+      assert.equal(result.metadata[1].name, 'value');
+      assert.equal(result.metadata[1].value, 'my-value');
+    });
   });
 
   describe('when it is passed params with a `file`', () => {
-    it('sets the Consul key to the value cited in the file and resolves the promise with the proper metadata', () => {
+    let result;
+
+    beforeEach(() => {
       mockPut('my-value-from-file');
 
       process.nextTick(() => {
-        stdin.send(JSON.stringify({
-          source: {
-            host: 'my-consul.com',
-            tls_cert: 'my-cert',
-            tls_key: 'my-cert-key',
-            token: 'my-token',
-            key: 'my/key'
-          },
-          params: {
-            file: 'test/fixtures/value_from_file'
-          }
+        stdin.send(sourceJson({
+          file: 'test/fixtures/value_from_file'
         }));
       });
 
       return outAction('.')
-        .then(result => {
-          assert.equal(result.metadata[0].name, 'value');
-          assert.equal(result.metadata[0].value, 'my-value-from-file');
+        .then(res => {
+          result = res;
         });
     });
+
+    it('sets the Consul key to the value cited in the file and resolves the promise with the proper version', () => {
+      assert.equal(result.version.value, 'my-value-from-file');
+    });
+
+    it('sets the Consul key to the value cited in the params.value and resolves the promise with metadata that includes a "timestamp"', () => {
+      assert.equal(result.metadata[0].name, 'timestamp');
+    });
+
+    it('sets the Consul key to the value cited in the params.value and resolves the promise with metadata that includes a "value"', () => {
+      assert.equal(result.metadata[1].name, 'value');
+      assert.equal(result.metadata[1].value, 'my-value-from-file');
+    });
   });
 });