diff --git a/apluslms_roman/cli.py b/apluslms_roman/cli.py
index b00f57d..34aed66 100644
--- a/apluslms_roman/cli.py
+++ b/apluslms_roman/cli.py
@@ -2,12 +2,17 @@
 from os import getcwd
 from os.path import abspath, expanduser, expandvars
 from sys import exit
+import logging
 
 from . import __version__
 from. builder import Engine
 from .backends.docker import DockerBackend
 from .configuration import CourseConfigError, CourseConfig
+from .validator import Validator
 
+LOG_LEVELS = [logging.WARNING, logging.INFO, logging.DEBUG]
+
+logger = logging.getLogger(__name__)
 
 def main():
     parser = argparse.ArgumentParser(description='Course material builder')
@@ -16,8 +21,15 @@ def main():
 
     parser.add_argument('--version', action='store_true',
                         help='Print version info')
+    parser.add_argument("-v", "--verbose", dest="verbose_count",
+                        action="count", default=0,
+                        help="increases log verbosity for each occurence.")
 
     args = parser.parse_args()
+    logging.basicConfig(
+        level=LOG_LEVELS[min(args.verbose_count, 2)],
+        #format='%(name)s (%(levelname)s): %(message)s'
+    )
 
     if args.version:
         print("Roman {}\n".format(__version__))
@@ -53,10 +65,21 @@ def main():
         print("Invalid course config: {}".format(e))
         exit(1)
 
+    # create validator (and validate config)
+    logging.info(" >> Validation step:")
+    validator = Validator(config)
+    # validation_result = validator.validate(location of the file here, "config", 1)
+    # if validation_result is False:
+    #    logging.warning( "Validation unsuccessful. Terminating.")
+    #    exit(0)
+    logging.info(" >> All files validated succesfully")
+
+
     # build course
     builder = engine.create_builder(config)
     result = builder.build()
     print(result)
+    logging.shutdown()
     exit(result.code or 0)
 
 
diff --git a/apluslms_roman/schemas/config_v1_0.yaml b/apluslms_roman/schemas/config_v1_0.yaml
new file mode 100644
index 0000000..7443a27
--- /dev/null
+++ b/apluslms_roman/schemas/config_v1_0.yaml
@@ -0,0 +1,68 @@
+---
+$schema: "http://json-schema.org/draft-04/schema"
+#$schema: "http://stsci.edu/schemas/yaml-schema/draft-01"
+title: Exercise schema
+type: object
+required:
+  - title
+  - description
+  - instructions
+  - view_type
+  - files
+  - container
+optional:
+  - radar_info
+
+definitions:
+  languageType:
+    type: string
+    enum:
+      - python
+      - scala
+      - javascript
+
+additionalProperties: false
+properties:
+  title:
+    description: The name of the exercise
+    type: string
+  description:
+    type: string
+  instructions:
+    type: string
+  view_type:
+    type: string
+  files:
+    type: array
+    items:
+      type: object
+      required:
+        - field
+      properties:
+        field:
+          type: string
+        name:
+          type: string
+  container:
+    type: object
+    properties:
+      image:
+        type: string
+      mount:
+        type: string
+      cmd:
+        type: string
+  radar_info:
+    type: object
+    required:
+      - tokenizer
+    properties:
+      tokenizer:
+        $ref: '#/definitions/languageType'
+        #enum:
+        #  - python
+        #  - scala
+        #  - javascript
+      minimum_match_tokens:
+        type: number
+        minimum: 0
diff --git a/apluslms_roman/schemas/config_v1_1.yaml b/apluslms_roman/schemas/config_v1_1.yaml
new file mode 100644
index 0000000..7443a27
--- /dev/null
+++ b/apluslms_roman/schemas/config_v1_1.yaml
@@ -0,0 +1,68 @@
+---
+$schema: "http://json-schema.org/draft-04/schema"
+#$schema: "http://stsci.edu/schemas/yaml-schema/draft-01"
+title: Exercise schema
+type: object
+required:
+  - title
+  - description
+  - instructions
+  - view_type
+  - files
+  - container
+optional:
+  - radar_info
+
+definitions:
+  languageType:
+    type: string
+    enum:
+      - python
+      - scala
+      - javascript
+
+additionalProperties: false
+properties:
+  title:
+    description: The name of the exercise
+    type: string
+  description:
+    type: string
+  instructions:
+    type: string
+  view_type:
+    type: string
+  files:
+    type: array
+    items:
+      type: object
+      required:
+        - field
+      properties:
+        field:
+          type: string
+        name:
+          type: string
+  container:
+    type: object
+    properties:
+      image:
+        type: string
+      mount:
+        type: string
+      cmd:
+        type: string
+  radar_info:
+    type: object
+    required:
+      - tokenizer
+    properties:
+      tokenizer:
+        $ref: '#/definitions/languageType'
+        #enum:
+        #  - python
+        #  - scala
+        #  - javascript
+      minimum_match_tokens:
+        type: number
+        minimum: 0
diff --git a/apluslms_roman/schemas/index_v1_0.yaml b/apluslms_roman/schemas/index_v1_0.yaml
new file mode 100644
index 0000000..6d8e7bb
--- /dev/null
+++ b/apluslms_roman/schemas/index_v1_0.yaml
@@ -0,0 +1,175 @@
+---
+$schema: "http://json-schema.org/draft-04/schema"
+title: Index schema
+type: object
+definitions:
+  dateTime:
+    type: string
+    pattern: ^\d{4}\-\d{2}\-\d{2}(\s\d{2}\:\d{2})?$
+  configFormat:
+    type: string
+    pattern: \.(json|yaml|yml)$
+  statusEnum:
+    type: string
+    enum:
+      - ready
+      - unlisted
+      - enrollment
+      - enrollment_ext
+      - hidden
+      - maintenance
+      - nototal
+
+
+required:
+  - categories
+  - end
+  - language
+  - modules
+  - name
+  - start
+  - static_dir
+
+additionalProperties: false
+properties:
+  categories:
+    type: object
+    description: Categories can be added freely
+    additionalProperties:
+      type: object
+      required:
+        - name
+      properties:
+        name:
+          type: string
+        status:
+          $ref: '#/definitions/statusEnum'
+  end:
+    $ref: '#/definitions/dateTime'
+  language:
+    type: string
+    enum:
+      - en
+      - fi
+  modules:
+    type: array
+    additionalItems: false
+    items:
+      type: object
+      required:
+        - children
+        - key
+        # muita pakollisia?
+      properties:
+        children:
+          type: array
+          additionalItems: false
+          items:
+            type: object
+            required:
+              - category
+              - key
+            #additionalProperties: false
+            properties:
+              category:
+                type: string
+              children:
+                type: array
+                additionalItems: false
+                items:
+                  type: object
+                  required:
+                    - category
+                  properties:
+                    category:
+                      type: string
+                    children:
+                      type: array
+                      additionalItems: false
+                      items:
+                        type: object
+                        required:
+                          - category
+                          - key
+                        #additionalProperties: false
+                        properties:
+                          allow_assistant_grading:
+                            type: boolean
+                          category:
+                            type: string
+                          config:
+                            $ref: '#/definitions/configFormat'
+                          confirm_the_level:
+                            type: boolean
+                          difficulty:
+                            type: string
+                          key:
+                            type: string
+                          lti:
+                            type: string
+                          lti_context_id:
+                            type: string
+                          lti_resource_link_id:
+                            type: string
+                          max_group_size:
+                            type: number
+                            minimum: 0
+                          max_points:
+                            type: number
+                            minimum: 0
+                          max_submissions:
+                            type: number
+                            minimum: 0
+                          min_group_size:
+                            type: number
+                            minimum: 0
+                          points_to_pass:
+                            type: number
+                            minimum: 0
+                          scale_points:
+                            type: number
+                          status:
+                            $ref: '#/definitions/statusEnum'
+                          title:
+                            type: string
+                    key:
+                      type: string
+                    name:
+                      type: string
+                    static_content:
+                      type: string
+                    use_wide_column:
+                      type: boolean
+
+              key:
+                type: string
+              name:
+                type: string
+              static_content:
+                type: string
+              status:
+                $ref: '#/definitions/statusEnum'
+              use_wide_column:
+                type: boolean
+        close:
+          $ref: '#/definitions/dateTime'
+        key:
+          type: string
+        late_close:
+          $ref: '#/definitions/dateTime'
+        late_penalty:
+          type: number
+          minimum: 0.0
+        name:
+          type: string
+        open:
+          $ref: '#/definitions/dateTime'
+        status:
+          $ref: '#/definitions/statusEnum'
+
+  name:
+    type: string
+  start:
+    $ref: '#/definitions/dateTime'
+  static_dir:
+    type: string
diff --git a/apluslms_roman/schemas/index_v1_1.yaml b/apluslms_roman/schemas/index_v1_1.yaml
new file mode 100644
index 0000000..6d8e7bb
--- /dev/null
+++ b/apluslms_roman/schemas/index_v1_1.yaml
@@ -0,0 +1,175 @@
+---
+$schema: "http://json-schema.org/draft-04/schema"
+title: Index schema
+type: object
+definitions:
+  dateTime:
+    type: string
+    pattern: ^\d{4}\-\d{2}\-\d{2}(\s\d{2}\:\d{2})?$
+  configFormat:
+    type: string
+    pattern: \.(json|yaml|yml)$
+  statusEnum:
+    type: string
+    enum:
+      - ready
+      - unlisted
+      - enrollment
+      - enrollment_ext
+      - hidden
+      - maintenance
+      - nototal
+
+
+required:
+  - categories
+  - end
+  - language
+  - modules
+  - name
+  - start
+  - static_dir
+
+additionalProperties: false
+properties:
+  categories:
+    type: object
+    description: Categories can be added freely
+    additionalProperties:
+      type: object
+      required:
+        - name
+      properties:
+        name:
+          type: string
+        status:
+          $ref: '#/definitions/statusEnum'
+  end:
+    $ref: '#/definitions/dateTime'
+  language:
+    type: string
+    enum:
+      - en
+      - fi
+  modules:
+    type: array
+    additionalItems: false
+    items:
+      type: object
+      required:
+        - children
+        - key
+        # muita pakollisia?
+      properties:
+        children:
+          type: array
+          additionalItems: false
+          items:
+            type: object
+            required:
+              - category
+              - key
+            #additionalProperties: false
+            properties:
+              category:
+                type: string
+              children:
+                type: array
+                additionalItems: false
+                items:
+                  type: object
+                  required:
+                    - category
+                  properties:
+                    category:
+                      type: string
+                    children:
+                      type: array
+                      additionalItems: false
+                      items:
+                        type: object
+                        required:
+                          - category
+                          - key
+                        #additionalProperties: false
+                        properties:
+                          allow_assistant_grading:
+                            type: boolean
+                          category:
+                            type: string
+                          config:
+                            $ref: '#/definitions/configFormat'
+                          confirm_the_level:
+                            type: boolean
+                          difficulty:
+                            type: string
+                          key:
+                            type: string
+                          lti:
+                            type: string
+                          lti_context_id:
+                            type: string
+                          lti_resource_link_id:
+                            type: string
+                          max_group_size:
+                            type: number
+                            minimum: 0
+                          max_points:
+                            type: number
+                            minimum: 0
+                          max_submissions:
+                            type: number
+                            minimum: 0
+                          min_group_size:
+                            type: number
+                            minimum: 0
+                          points_to_pass:
+                            type: number
+                            minimum: 0
+                          scale_points:
+                            type: number
+                          status:
+                            $ref: '#/definitions/statusEnum'
+                          title:
+                            type: string
+                    key:
+                      type: string
+                    name:
+                      type: string
+                    static_content:
+                      type: string
+                    use_wide_column:
+                      type: boolean
+
+              key:
+                type: string
+              name:
+                type: string
+              static_content:
+                type: string
+              status:
+                $ref: '#/definitions/statusEnum'
+              use_wide_column:
+                type: boolean
+        close:
+          $ref: '#/definitions/dateTime'
+        key:
+          type: string
+        late_close:
+          $ref: '#/definitions/dateTime'
+        late_penalty:
+          type: number
+          minimum: 0.0
+        name:
+          type: string
+        open:
+          $ref: '#/definitions/dateTime'
+        status:
+          $ref: '#/definitions/statusEnum'
+
+  name:
+    type: string
+  start:
+    $ref: '#/definitions/dateTime'
+  static_dir:
+    type: string
diff --git a/apluslms_roman/validator.py b/apluslms_roman/validator.py
new file mode 100644
index 0000000..6bf0521
--- /dev/null
+++ b/apluslms_roman/validator.py
@@ -0,0 +1,97 @@
+import yaml
+from jsonschema import validate, ValidationError
+import re
+import os
+#from operator import itemgetter
+import logging
+
+logger = logging.getLogger(__name__)
+
+#List of (possible) custom schema locations will be in config file
+def get_folders(config):
+    folders = config.__config__.get("schema_path", [])
+    if not isinstance(folders, list):
+        raise ValueError("Invalid type for 'schema_path' in config. Excpected a list.")
+    dir_, _ = os.path.split(__file__)
+    folders.append(os.path.join(dir_, "schemas"))
+    return folders
+
+#Format of index:  { schema_name: {(major, minor): full_filepath}}
+SCHEMA_INDEX = {}
+
+class Validator:
+    def __init__(self, config):
+        logger.info(" Creating validator.")
+        self.folders = get_folders(config)
+        logger.info(" Validator ready.")
+
+    def validate(self, filename, schema, major=1, minor=None):
+        logger.info(" Preparing to validate %s...", filename)
+        logger.info(" Locating all valid schemas...")
+        self.find_all_matches(schema)
+        logger.info(" Locating matching version v%d...", major)
+        serial, schema_path = self.find_newest(schema, major, minor)
+        #schema_fullname = "{}_v{}_{}".format(schema, serial[0], serial[1])
+        #schema_path = os.path.join(ext[0], schema_fullname)
+        logger.info(" Starting validation of %s with %s", filename, schema_path)
+        return self.assert_valid(schema_path, filename)
+
+
+    def find_all_matches(self, schema):
+        prog = re.compile("{}_v(\d+)_(\d+).(yaml|yml|json)".format(schema))
+        logger.debug(" Looking for schema-------------%s", schema)
+        for folder in self.folders:
+            logger.debug(" Folder-------------%s",  folder)
+            for ff in os.listdir(folder):
+                logger.debug(" File-------------%s",  ff)
+                if prog.match(ff) is not None:
+                    major, minor, ext = prog.match(ff).groups()
+                    schema_i = SCHEMA_INDEX.setdefault(schema, {})
+                    logger.debug(" Index-------------%s",  SCHEMA_INDEX)
+                    current = schema_i.setdefault((int(major), int(minor)), None)
+                    if current is None:
+                        schema_i[int(major), int(minor)] = os.path.join(folder, ff)
+
+    #Finds the newest schema with given 'major' and newest 'minor'.
+    #If major is not defined, v1 is assumed.
+    def find_newest(self, schema, major, minor):
+        schemas = SCHEMA_INDEX.get(schema)
+        if schemas is None:
+            logger.warning(" No schema's with that name!")
+            return None
+
+        if minor is None:
+            ver = max({v for v in schemas if v[0]==major}, default=None)
+            if ver is None:
+                logger.warning(" No schema with version %d", major)
+                return None
+        else:
+            ver = (major, minor)
+
+        _file = schemas.get(ver, None)
+        if _file is None:
+            logger.warning(" No schema with version %d.%d", major, minor)
+            return None
+        return ver, _file
+
+
+    #Validate schema
+    def assert_valid(self, schema, filename):
+        try:
+            with open(filename, "r") as f:
+                ff = f.read()
+            with open(schema, "r") as s:
+                ss = s.read()
+        except:
+            logger.exception(' Error with files, exiting....')
+            return False
+
+        try:
+            logger.info(' Files opened succesfully. Validating...')
+            validate(yaml.safe_load(ff), yaml.safe_load(ss))
+            logger.info(' %s validated succesfully', filename)
+            return True
+        except ValidationError as e:
+            logger.warning(" An error occurred!")
+            logger.warning(" %s", e)
+            return False
diff --git a/requirements.txt b/requirements.txt
index c32bca5..11748dc 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,2 +1,3 @@
 PyYaml>=3.12
 Docker>=3.0.0
+jsonschema>=2.6.0 
diff --git a/requirements_build_linux.txt b/requirements_build_linux.txt
index 64faff7..4241414 100644
--- a/requirements_build_linux.txt
+++ b/requirements_build_linux.txt
@@ -1 +1,2 @@
 PyInstaller >= 3.2.1
+tk
diff --git a/simple_gui/setup.py b/simple_gui/setup.py
index 8070692..b82fce9 100755
--- a/simple_gui/setup.py
+++ b/simple_gui/setup.py
@@ -49,7 +49,7 @@
     ],
 
     zip_safe=True,
-    #packages=find_packages(exclude=['contrib', 'docs', 'tests']),
+    packages=find_packages(exclude=['contrib', 'docs', 'tests']),
     py_modules=['roman_tki'],
     include_package_data = True,
     package_data={