diff --git a/Devel.hs b/Devel.hs
--- a/Devel.hs
+++ b/Devel.hs
@@ -77,9 +77,10 @@
 #if MIN_VERSION_http_reverse_proxy(0, 2, 0)
 import qualified Network.HTTP.ReverseProxy             as ReverseProxy
 #endif
-import           Network.HTTP.Types                    (status200)
+import           Network.HTTP.Types                    (status200, status503)
 import           Network.Socket                        (sClose)
-import           Network.Wai                           (responseLBS)
+import           Network.Wai                           (responseLBS, requestHeaders)
+import           Network.Wai.Parse                     (parseHttpAccept)
 import           Network.Wai.Handler.Warp              (run)
 import           SrcLoc                                (Located)
 import           Data.FileEmbed        (embedFile)
@@ -135,11 +136,18 @@
     manager <- newManager def
 #endif
     let refreshHtml = LB.fromChunks $ return $(embedFile "refreshing.html")
-    let onExc _ _ = return $ responseLBS status200
-            [ ("content-type", "text/html")
-            , ("Refresh", "1")
-            ]
-            refreshHtml
+    let onExc _ req
+            | maybe False (("application/json" `elem`) . parseHttpAccept)
+                (lookup "accept" $ requestHeaders req) =
+                    return $ responseLBS status503
+                        [ ("Retry-After", "1")
+                        ]
+                        "{\"message\":\"Recompiling\"}"
+            | otherwise = return $ responseLBS status200
+                [ ("content-type", "text/html")
+                , ("Refresh", "1")
+                ]
+                refreshHtml
 
     let runProxy =
             run (develPort opts) $ waiProxyToSettings
diff --git a/yesod-bin.cabal b/yesod-bin.cabal
--- a/yesod-bin.cabal
+++ b/yesod-bin.cabal
@@ -1,5 +1,5 @@
 name:            yesod-bin
-version:         1.2.9
+version:         1.2.9.1
 license:         MIT
 license-file:    LICENSE
 author:          Michael Snoyman <michael@snoyman.com>
@@ -91,6 +91,7 @@
                      , transformers
                      , warp               >= 1.3.7.5
                      , wai                >= 1.4
+                     , wai-extra
                      , data-default-class
                      , streaming-commons