diff --git a/src/Main.elm b/src/Main.elm
index 0468319..92898f2 100644
--- a/src/Main.elm
+++ b/src/Main.elm
@@ -13,6 +13,7 @@ import Bergamot.Latex exposing (..)
 import Bergamot.ObjectLanguage exposing (topLevelExpr, exprToTerm)
 import Bergamot.Utils exposing (..)
 import Json.Encode
+import Json.Decode exposing (string, field, list, oneOf, succeed, fail)
 import Maybe
 import Tuple
 
@@ -32,13 +33,7 @@ tabEq t1 t2 =
 type EditMode
     = Query
     | Syntax
-
-editModeEq : EditMode -> EditMode -> Bool
-editModeEq m1 m2 =
-    case (m1, m2) of
-        (Query, Query) -> True
-        (Syntax, Syntax) -> True
-        _ -> False
+    | Custom String
 
 type ResultMode
     = Conclusion
@@ -57,20 +52,57 @@ type alias Model =
     , inputProgram : String
     , tab : Tab
     , query : String
-    , editMode : EditMode
+    , inputModes : List (String, EditMode)
+    , inputMode : Int
     , resultMode : ResultMode
     }
-type alias Flags = { renderRules: String, inputRules: String, rules: String, query: String }
+type alias Flags =
+    { renderRules : String
+    , inputRules : String
+    , rules : String
+    , query : String
+    , inputModes : Json.Decode.Value
+    }
 type Msg
     = SetProgram String
     | SetRenderProgram String
     | SetQuery String
     | SetTab Tab
-    | SetEditMode EditMode
+    | SetInputMode Int
     | SetResultMode ResultMode
 
+decodeInputModes: Json.Decode.Value -> List (String, EditMode)
+decodeInputModes val =
+    let
+        exactString s1 v =
+            string
+            |> Json.Decode.andThen (\s2 -> if s1 == s2
+                                           then succeed v
+                                           else Json.Decode.fail "did not match expected string")
+        editModeDecoder = oneOf
+            [ exactString "query" Query
+            , exactString "syntax" Syntax
+            , field "custom" string |> Json.Decode.map Custom
+            ]
+        decoder = Json.Decode.keyValuePairs editModeDecoder
+    in
+        case Json.Decode.decodeValue decoder val of
+            Ok l -> l
+            Err _ -> [("Query", Query), ("Language Term", Syntax)]
+
 init : Flags -> (Model, Cmd Msg)
-init fs = ({ program = fs.rules, renderProgram = fs.renderRules, inputProgram = fs.inputRules, query = fs.query, tab = Rendered, editMode = Syntax, resultMode = Conclusion }, Cmd.none)
+init fs =
+    ( { program = fs.rules
+      , renderProgram = fs.renderRules
+      , inputProgram = fs.inputRules
+      , query = fs.query
+      , tab = Rendered
+      , inputModes = decodeInputModes fs.inputModes
+      , inputMode = 0
+      , resultMode = Conclusion
+      }
+    , Cmd.none
+    )
 
 viewSection : String -> Html Msg -> Html Msg
 viewSection name content =
@@ -83,23 +115,23 @@ viewTab tab editor metaEditor rendered =
         MetaEditor -> metaEditor
         Rendered -> rendered
 
-viewSelector : (a -> a -> Bool) -> (a -> Msg) -> a -> List (a, String) -> Html Msg
+viewSelector : (Int -> a -> b -> Bool) -> (Int -> a -> Msg) -> b -> List (a, String) -> Html Msg
 viewSelector eq mkMsg mode modeNames =
     Html.div [ class "bergamot-selector" ] <|
-        List.map (\(modep, name) ->
+        List.indexedMap (\idx (modep, name) ->
             Html.button
-                [ classList [("active", eq mode modep)]
-                , onClick (mkMsg modep)
+                [ classList [("active", eq idx modep mode)]
+                , onClick (mkMsg idx modep)
                 ] [ Html.text name ]) modeNames
 
 viewTabSelector : Tab -> List (Tab, String) -> Html Msg
-viewTabSelector = viewSelector tabEq SetTab
+viewTabSelector = viewSelector (\_ -> tabEq) (\_ -> SetTab)
 
-viewEditModeSelector : EditMode -> List (EditMode, String) -> Html Msg
-viewEditModeSelector = viewSelector editModeEq SetEditMode
+viewInputModeSelector : Int -> List (EditMode, String) -> Html Msg
+viewInputModeSelector = viewSelector (\i _ idx -> i == idx) (\idx _ -> SetInputMode idx)
 
 viewResultModeSelector : ResultMode -> List (ResultMode, String) -> Html Msg
-viewResultModeSelector = viewSelector resultModeEq SetResultMode
+viewResultModeSelector = viewSelector (\_ -> resultModeEq) (\_ -> SetResultMode)
 
 viewRule : RuleEnv -> Rule -> Maybe (Html Msg)
 viewRule env r = renderRuleViaRules env r
@@ -130,6 +162,7 @@ type Error
     | BadProg
     | BadRenderProg
     | FailedRender
+    | InvalidInputMode
     | Silent
 
 combineTwoResults : (a -> b -> Result Error c) -> Result Error a -> Result Error b -> Result Error c
@@ -151,6 +184,7 @@ errorToString err =
         BadProg -> "Unable to parse rules"
         BadRenderProg -> "Unable to parse rendering rules"
         FailedRender -> "Unable to render terms using provided rendering rules"
+        InvalidInputMode -> "Invalid edit mode specified"
         Silent -> ""
 
 viewError : Error -> Html Msg
@@ -170,6 +204,13 @@ viewOrError r =
         Err e -> Html.div [] [ viewError e ] -- The div wrapper is needed because Elm has a bug?
         Ok html -> html
 
+getEditMode : Int -> List (String, EditMode) -> Result Error EditMode
+getEditMode i l =
+    case l of
+        [] -> Err InvalidInputMode
+        ((_, editMode) :: xs) ->
+            if i == 0 then Ok editMode else getEditMode (i - 1) xs
+
 proofGoal : EditMode -> String -> String -> Result Error (Term Metavariable)
 proofGoal editMode inputProgs querys =
     if querys == ""
@@ -196,6 +237,7 @@ proofGoal editMode inputProgs querys =
                                 _ -> Err NoConversionResults
                     (_, Nothing) -> Err BadObjectTerm
                     (Nothing, _) -> Err BadInputProg
+            Custom _ -> Err BadInputProg
 
 progAndRenderProg : String -> String -> Result Error (RuleEnv, RuleEnv)
 progAndRenderProg progs renderProgs =
@@ -227,13 +269,15 @@ viewProofTree resultMode query (prog, renderProg) =
 view : Model -> Html Msg
 view m =
     let
-        termOrErr = proofGoal m.editMode m.inputProgram m.query
+        mode = getEditMode m.inputMode m.inputModes
+        termOrErr = mode |> Result.andThen (\editMode -> proofGoal editMode m.inputProgram m.query)
         progsOrErr = progAndRenderProg m.program m.renderProgram
         proofTreeOrErr = combineTwoResults (viewProofTree m.resultMode) termOrErr progsOrErr
     in
         Html.div [ class "bergamot-root" ]
         [ viewSection "Input" <| Html.div [] <|
-            [ viewEditModeSelector m.editMode [(Query, "Query"), (Syntax, "Language Term")]
+            [ viewInputModeSelector m.inputMode <|
+                List.map (\(a, b) -> (b, a)) m.inputModes
             , Html.input [ type_ "text", onInput SetQuery, value m.query ] []
             ] ++
             viewIfError termOrErr
@@ -258,7 +302,7 @@ update msg m =
         SetRenderProgram prog -> ({ m | renderProgram = prog }, Cmd.none)
         SetQuery query -> ({ m | query = query }, Cmd.none)
         SetTab tab -> ({ m | tab = tab }, Cmd.none)
-        SetEditMode mode -> ({ m | editMode = mode }, Cmd.none)
+        SetInputMode mode -> ({ m | inputMode = mode }, Cmd.none)
         SetResultMode mode -> ({ m | resultMode = mode }, Cmd.none)
 
 subscriptions : Model -> Sub Msg