diff --git a/dgs/diagrams.py b/dgs/diagrams.py
index f81eb80..5808aec 100644
--- a/dgs/diagrams.py
+++ b/dgs/diagrams.py
@@ -183,11 +183,11 @@ def asJson(self, baseurl):
         else:
             jsonTxt = """{
   "diagrams": {
-    "png": {
-      "url": "%s/png/%s.png"
+    "%s": {
+      "url": "%s/%s/%s.%s"
     }
   }
-}""" % (baseurl,self.crc32)
+}""" % (self.outputType,baseurl,self.outputType,self.crc32,self.outputType)
         return jsonTxt
 
         
diff --git a/dgs/webserver.py b/dgs/webserver.py
index 66b11d9..cc09576 100644
--- a/dgs/webserver.py
+++ b/dgs/webserver.py
@@ -47,19 +47,24 @@ def render(outputType,crc32):
     filename="%s.%s" % (crc32,outputType)
     return send_from_directory(outputDirectory,filename)
 
+def getParam(name):
+    value=request.form.get(name)
+    if value is None:
+        value=request.args.get(name)
+    return value
+
 @app.route('/render', methods=['POST'])
 def renderForWikiExtension():
     """ endpoint for diagrams extension"""
-    generator=request.form.get('generator')
-    source=request.form.get('source')
-    types=request.form.get('types')
+    generator=getParam('generator')
+    source=getParam('source')
+    format=getParam('types')
     gen=Generators.get(generator)
     ip=request.remote_addr
-    result=gen.generate('dot',source,'png')
+    result=gen.generate('dot',source,format)
     json=result.asJson(request.base_url)
     return json
     
-    
 @app.route('/diagrams', methods=['GET', 'POST']) #allow both GET and POST requests
 def form_example():
     err=None
diff --git a/tests/test_diagrams.py b/tests/test_diagrams.py
index 4b8779e..38f6aff 100644
--- a/tests/test_diagrams.py
+++ b/tests/test_diagrams.py
@@ -4,6 +4,7 @@
 @author: wf
 '''
 import unittest
+import os
 from dgs.diagrams import Command,Generator,Generators,Example
 debug=True
 class TestDiagrams(unittest.TestCase):
@@ -70,11 +71,20 @@ def testGenerators(self):
                 assert valid
             
     def testGenerateResult(self):
+        '''
+        test provoked error
+        '''
         genid=Generators.generatorIdForAlias("plantuml")
         gen=Generators.get(genid)
         # provoke an error
         result=gen.generate('unknownalias','garbage input',gen.defaultType)    
         json=result.asJson('http://www.doe.com') 
+        print (json)
+        # there is an image version of the error
+        assert os.path.isfile(result.path)
+        # which needs to be remove to make the test reproducible
+        os.remove(result.path)
+        
         assert "error" in json
                     
     def testDecodeImage(self):