diff --git a/src/DiffOutput.hs b/src/DiffOutput.hs
index 6fd0bb386..8516a0ee9 100644
--- a/src/DiffOutput.hs
+++ b/src/DiffOutput.hs
@@ -1,24 +1,35 @@
 module DiffOutput where
 
-import qualified Data.ByteString.Lazy as B
-import qualified Data.Text.Lazy.IO as TextIO
+import qualified Data.Text.IO as TextIO
 import Data.Functor.Both
 import Diffing
 import Parser
 import qualified Renderer.JSON as J
 import qualified Renderer.Patch as P
+import Renderer
 import Renderer.Split
 import Source
 import System.Directory
 import System.FilePath
 import qualified System.IO as IO
+import Data.String
+import Data.Text hiding (split)
 
--- | The available types of diff rendering.
-data Format = Split | Patch | JSON
+-- | Returns a rendered diff given a parser, diff arguments and two source blobs.
+textDiff :: Parser -> DiffArguments -> Both SourceBlob -> IO Text
+textDiff parser arguments sources = case format arguments of
+  Split -> diffFiles parser split sources
+  Patch -> diffFiles parser P.patch sources
+  JSON -> diffFiles parser J.json sources
 
-data DiffArguments = DiffArguments { format :: Format, output :: Maybe FilePath, outputPath :: FilePath }
+-- | Returns a truncated diff given diff arguments and two source blobs.
+truncatedDiff :: DiffArguments -> Both SourceBlob -> IO Text
+truncatedDiff arguments sources = case format arguments of
+  Split -> return ""
+  Patch -> return $ P.truncatePatch arguments sources
+  JSON -> return "{}"
 
--- | Return a renderer from the command-line arguments that will print the diff.
+-- | Prints a rendered diff to stdio or a filepath given a parser, diff arguments and two source blobs.
 printDiff :: Parser -> DiffArguments -> Both SourceBlob -> IO ()
 printDiff parser arguments sources = case format arguments of
   Split -> put (output arguments) =<< diffFiles parser split sources
@@ -30,5 +41,5 @@ printDiff parser arguments sources = case format arguments of
                          then path </> (takeFileName outputPath -<.> ".html")
                          else path
         IO.withFile outputPath IO.WriteMode (`TextIO.hPutStr` rendered)
-  Patch -> putStr =<< diffFiles parser P.patch sources
-  JSON -> B.putStr =<< diffFiles parser J.json sources
+  Patch -> TextIO.putStr =<< diffFiles parser P.patch sources
+  JSON -> TextIO.putStr =<< diffFiles parser J.json sources
diff --git a/src/Diffing.hs b/src/Diffing.hs
index 63730807b..a3440dbd6 100644
--- a/src/Diffing.hs
+++ b/src/Diffing.hs
@@ -70,9 +70,11 @@ readAndTranscodeFile path = do
 
 -- | Given a parser and renderer, diff two sources and return the rendered
 -- | result.
-diffFiles :: Parser -> Renderer T.Text b -> Both SourceBlob -> IO b
+-- | Returns the rendered result strictly, so it's always fully evaluated
+-- | with respect to other IO actions.
+diffFiles :: Parser -> Renderer T.Text -> Both SourceBlob -> IO T.Text
 diffFiles parser renderer sourceBlobs = do
   let sources = source <$> sourceBlobs
   terms <- sequence $ parser <$> sources
   let replaceLeaves = breakDownLeavesByWord <$> sources
-  return $ renderer (runBothWith diffTerms $ replaceLeaves <*> terms) sourceBlobs
+  return $! renderer (runBothWith diffTerms $ replaceLeaves <*> terms) sourceBlobs
diff --git a/src/Renderer.hs b/src/Renderer.hs
index ea381c406..740e1a236 100644
--- a/src/Renderer.hs
+++ b/src/Renderer.hs
@@ -4,6 +4,12 @@ import Data.Functor.Both
 import Diff
 import Info
 import Source
+import Data.Text
 
 -- | A function that will render a diff, given the two source files.
-type Renderer a b = Diff a Info -> Both SourceBlob -> b
+type Renderer a = Diff a Info -> Both SourceBlob -> Text
+
+data DiffArguments = DiffArguments { format :: Format, output :: Maybe FilePath, outputPath :: FilePath }
+
+-- | The available types of diff rendering.
+data Format = Split | Patch | JSON
diff --git a/src/Renderer/JSON.hs b/src/Renderer/JSON.hs
index 15ebdda4c..6fe79f013 100644
--- a/src/Renderer/JSON.hs
+++ b/src/Renderer/JSON.hs
@@ -9,12 +9,13 @@ import Category
 import Control.Comonad.Cofree
 import Control.Monad.Free
 import Data.Aeson hiding (json)
+import Data.Aeson.Encode
 import Data.Bifunctor.Join
-import Data.ByteString.Builder
-import Data.ByteString.Lazy
 import Data.Functor.Both
-import Data.Monoid
 import Data.OrderedMap hiding (fromList)
+import Data.Text
+import Data.Text.Lazy (toStrict)
+import Data.Text.Lazy.Builder (toLazyText)
 import qualified Data.Text as T
 import Data.Vector hiding (toList)
 import Diff
@@ -28,11 +29,8 @@ import Syntax
 import Term
 
 -- | Render a diff to a string representing its JSON.
-json :: Renderer a ByteString
-json diff sources = toLazyByteString . fromEncoding . pairs $
-     "rows" .= annotateRows (splitDiffByLines (source <$> sources) diff)
-  <> "oids" .= (oid <$> sources)
-  <> "paths" .= (path <$> sources)
+json :: Renderer a
+json diff sources = toStrict . toLazyText . encodeToTextBuilder $ object ["rows" .= annotateRows (splitDiffByLines (source <$> sources) diff), "oids" .= (oid <$> sources), "paths" .= (path <$> sources)]
   where annotateRows = fmap (fmap NumberedLine) . numberedRows
 
 newtype NumberedLine a = NumberedLine (Int, Line a)
diff --git a/src/Renderer/Patch.hs b/src/Renderer/Patch.hs
index 18e9d14fa..00da9460e 100644
--- a/src/Renderer/Patch.hs
+++ b/src/Renderer/Patch.hs
@@ -1,7 +1,8 @@
 module Renderer.Patch (
   patch,
   hunks,
-  Hunk(..)
+  Hunk(..),
+  truncatePatch
 ) where
 
 import Alignment
@@ -21,10 +22,15 @@ import Data.Functor.Both as Both
 import Data.List
 import Data.Maybe
 import Data.Monoid
+import Data.Text (pack, Text)
+
+-- | Render a timed out file as a truncated diff.
+truncatePatch :: DiffArguments -> Both SourceBlob -> Text
+truncatePatch arguments blobs = pack $ header blobs ++ "#timed_out\nTruncating diff: timeout reached.\n"
 
 -- | Render a diff in the traditional patch format.
-patch :: Renderer a String
-patch diff blobs = case getLast $ foldMap (Last . Just) string of
+patch :: Renderer a
+patch diff blobs = pack $ case getLast (foldMap (Last . Just) string) of
   Just c | c /= '\n' -> string ++ "\n\\ No newline at end of file\n"
   _ -> string
   where string = header blobs ++ mconcat (showHunk blobs <$> hunks diff blobs)
@@ -108,13 +114,17 @@ header blobs = intercalate "\n" [filepathHeader, fileModeHeader, beforeFilepath,
         (oidA, oidB) = runBoth $ oid <$> blobs
         (modeA, modeB) = runBoth $ blobKind <$> blobs
 
+-- | A hunk representing no changes.
+emptyHunk :: Hunk (SplitDiff a Info)
+emptyHunk = Hunk { offset = mempty, changes = [], trailingContext = [] }
+
 -- | Render a diff as a series of hunks.
-hunks :: Renderer a [Hunk (SplitDiff a Info)]
+hunks :: Diff a Info -> Both SourceBlob -> [Hunk (SplitDiff a Info)]
 hunks _ blobs | sources <- source <$> blobs
               , sourcesEqual <- runBothWith (==) sources
               , sourcesNull <- runBothWith (&&) (null <$> sources)
               , sourcesEqual || sourcesNull
-  = [Hunk { offset = mempty, changes = [], trailingContext = [] }]
+  = [emptyHunk]
 hunks diff blobs = hunksInRows (Join (1, 1)) $ fmap (fmap Prelude.fst) <$> splitDiffByLines (source <$> blobs) diff
 
 -- | Given beginning line numbers, turn rows in a split diff into hunks in a
diff --git a/src/Renderer/Split.hs b/src/Renderer/Split.hs
index 98827dec3..d9a9ae7cb 100644
--- a/src/Renderer/Split.hs
+++ b/src/Renderer/Split.hs
@@ -8,6 +8,7 @@ import Control.Monad.Free
 import Data.Foldable
 import Data.Functor.Both
 import Data.Monoid
+import qualified Data.Text as T
 import qualified Data.Text.Lazy as TL
 import Diff
 import Info
@@ -52,8 +53,8 @@ splitPatchToClassName patch = stringValue $ "patch " ++ case patch of
   SplitReplace _ -> "replace"
 
 -- | Render a diff as an HTML split diff.
-split :: Renderer leaf TL.Text
-split diff blobs = renderHtml
+split :: Renderer leaf
+split diff blobs = TL.toStrict . renderHtml
   . docTypeHtml
     . ((head $ link ! A.rel "stylesheet" ! A.href "style.css") <>)
     . body
diff --git a/test/CorpusSpec.hs b/test/CorpusSpec.hs
index c3dcc309a..5f26f9182 100644
--- a/test/CorpusSpec.hs
+++ b/test/CorpusSpec.hs
@@ -34,22 +34,17 @@ spec = parallel $ do
     examples "test/diffs/" `shouldNotReturn` []
 
   where
-    runTestsIn :: String -> (String -> String -> Expectation) -> SpecWith ()
+    runTestsIn :: String -> (T.Text -> T.Text -> Expectation) -> SpecWith ()
     runTestsIn directory matcher = do
       paths <- runIO $ examples directory
       let tests = correctTests =<< paths
       mapM_ (\ (formatName, renderer, paths, output) -> it (normalizeName (fst paths) ++ " (" ++ formatName ++ ")") $ testDiff renderer paths output matcher) tests
 
-    correctTests :: (Both FilePath, Maybe FilePath, Maybe FilePath, Maybe FilePath) -> [(String, Renderer a String, Both FilePath, Maybe FilePath)]
+    correctTests :: (Both FilePath, Maybe FilePath, Maybe FilePath, Maybe FilePath) -> [(String, Renderer a, Both FilePath, Maybe FilePath)]
     correctTests paths@(_, Nothing, Nothing, Nothing) = testsForPaths paths
     correctTests paths = List.filter (\(_, _, _, output) -> isJust output) $ testsForPaths paths
-    testsForPaths :: (Both FilePath, Maybe FilePath, Maybe FilePath, Maybe FilePath) -> [(String, Renderer a String, Both FilePath, Maybe FilePath)]
-    testsForPaths (paths, json, patch, split) = [ ("json", testJSON, paths, json), ("patch", P.patch, paths, patch), ("split", testSplit, paths, split) ]
-    testSplit :: Renderer a String
-    testSplit diff sources = TL.unpack $ Split.split diff sources
-    testJSON :: Renderer a String
-    testJSON diff sources = B.unpack $ J.json diff sources
-
+    testsForPaths :: (Both FilePath, Maybe FilePath, Maybe FilePath, Maybe FilePath) -> [(String, Renderer a, Both FilePath, Maybe FilePath)]
+    testsForPaths (paths, json, patch, split) = [ ("json", J.json, paths, json), ("patch", P.patch, paths, patch), ("split", Split.split, paths, split) ]
 
 -- | Return all the examples from the given directory. Examples are expected to
 -- | have the form "foo.A.js", "foo.B.js", "foo.patch.js". Diffs are not
@@ -75,14 +70,14 @@ normalizeName path = addExtension (dropExtension $ dropExtension path) (takeExte
 -- | Given file paths for A, B, and, optionally, a diff, return whether diffing
 -- | the files will produce the diff. If no diff is provided, then the result
 -- | is true, but the diff will still be calculated.
-testDiff :: Renderer T.Text String -> Both FilePath -> Maybe FilePath -> (String -> String -> Expectation) -> Expectation
+testDiff :: Renderer T.Text -> Both FilePath -> Maybe FilePath -> (T.Text -> T.Text -> Expectation) -> Expectation
 testDiff renderer paths diff matcher = do
-  let parser = parserForFilepath (fst paths)
   sources <- sequence $ readAndTranscodeFile <$> paths
-  let sourceBlobs = both S.SourceBlob S.SourceBlob <*> sources <*> pure mempty <*> paths <*> pure (Just S.defaultPlainBlob)
-  actual <- diffFiles parser renderer sourceBlobs
+  actual <- diffFiles parser renderer (sourceBlobs sources)
   case diff of
     Nothing -> matcher actual actual
     Just file -> do
-      expected <- readFile file
+      expected <- T.pack <$> readFile file
       matcher actual expected
+  where parser = parserForFilepath (fst paths)
+        sourceBlobs sources = pure S.SourceBlob <*> sources <*> pure mempty <*> paths <*> pure (Just S.defaultPlainBlob)
diff --git a/test/diffs/dictionary.json.js b/test/diffs/dictionary.json.js
index 0fd2f4ee8..fe957e0cc 100644
--- a/test/diffs/dictionary.json.js
+++ b/test/diffs/dictionary.json.js
@@ -1 +1 @@
-{"rows":[[{"number":1,"terms":[{"range":[0,2],"categories":["program"],"children":[{"range":[0,2],"categories":["expression_statement"],"children":[{"range":[0,2],"categories":["DictionaryLiteral"],"children":{}}]}]}],"range":[0,2],"hasChanges":false},{"number":1,"terms":[{"range":[0,2],"categories":["program"],"children":[{"range":[0,2],"categories":["expression_statement"],"children":[{"range":[0,2],"categories":["DictionaryLiteral"],"children":{}}]}]}],"range":[0,2],"hasChanges":false}],[{"number":2,"terms":[{"range":[2,12],"categories":["program"],"children":[{"range":[2,12],"categories":["expression_statement"],"children":[{"range":[2,12],"categories":["DictionaryLiteral"],"children":{"\"b\"":{"range":[4,10],"categories":["Pair"],"children":[{"range":[4,7],"categories":["StringLiteral"],"children":[{"range":[4,5],"categories":["StringLiteral"]},{"range":[5,6],"categories":["StringLiteral"]},{"range":[6,7],"categories":["StringLiteral"]}]},{"patch":"replace","range":[9,10],"categories":["number"]}]}}}]}]}],"range":[2,12],"hasChanges":true},{"number":2,"terms":[{"range":[2,12],"categories":["program"],"children":[{"range":[2,12],"categories":["expression_statement"],"children":[{"range":[2,12],"categories":["DictionaryLiteral"],"children":{"\"b\"":{"range":[4,10],"categories":["Pair"],"children":[{"range":[4,7],"categories":["StringLiteral"],"children":[{"range":[4,5],"categories":["StringLiteral"]},{"range":[5,6],"categories":["StringLiteral"]},{"range":[6,7],"categories":["StringLiteral"]}]},{"patch":"replace","range":[9,10],"categories":["number"]}]}}}]}]}],"range":[2,12],"hasChanges":true}],[{"number":3,"terms":[{"range":[12,21],"categories":["program"],"children":[{"range":[12,21],"categories":["expression_statement"],"children":[{"range":[12,21],"categories":["DictionaryLiteral"],"children":{"\"a\"":{"range":[14,20],"categories":["Pair"],"children":[{"range":[14,17],"categories":["StringLiteral"],"children":[{"range":[14,15],"categories":["StringLiteral"]},{"range":[15,16],"categories":["StringLiteral"]},{"range":[16,17],"categories":["StringLiteral"]}]},{"range":[19,20],"categories":["number"]}]}}}]}]}],"range":[12,21],"hasChanges":false},{"number":3,"terms":[{"range":[12,21],"categories":["program"],"children":[{"range":[12,21],"categories":["expression_statement"],"children":[{"range":[12,21],"categories":["DictionaryLiteral"],"children":{"\"a\"":{"range":[14,20],"categories":["Pair"],"children":[{"range":[14,17],"categories":["StringLiteral"],"children":[{"range":[14,15],"categories":["StringLiteral"]},{"range":[15,16],"categories":["StringLiteral"]},{"range":[16,17],"categories":["StringLiteral"]}]},{"range":[19,20],"categories":["number"]}]}}}]}]}],"range":[12,21],"hasChanges":false}],[{"number":4,"terms":[{"range":[21,23],"categories":["program"],"children":[{"range":[21,23],"categories":["expression_statement"],"children":[{"range":[21,22],"categories":["DictionaryLiteral"],"children":{}}]}]}],"range":[21,23],"hasChanges":false},{"number":4,"terms":[{"range":[21,23],"categories":["program"],"children":[{"range":[21,23],"categories":["expression_statement"],"children":[{"range":[21,22],"categories":["DictionaryLiteral"],"children":{}}]}]}],"range":[21,23],"hasChanges":false}],[{"number":5,"terms":[{"range":[23,23],"categories":["program"],"children":[{"range":[23,23],"categories":["expression_statement"],"children":[]}]}],"range":[23,23],"hasChanges":false},{"number":5,"terms":[{"range":[23,23],"categories":["program"],"children":[{"range":[23,23],"categories":["expression_statement"],"children":[]}]}],"range":[23,23],"hasChanges":false}]],"oids":["",""],"paths":["test/diffs/dictionary.A.js","test/diffs/dictionary.B.js"]}
\ No newline at end of file
+{"rows":[[{"terms":[{"children":[{"children":[{"children":{},"categories":["DictionaryLiteral"],"range":[0,2]}],"categories":["expression_statement"],"range":[0,2]}],"categories":["program"],"range":[0,2]}],"hasChanges":false,"range":[0,2],"number":1},{"terms":[{"children":[{"children":[{"children":{},"categories":["DictionaryLiteral"],"range":[0,2]}],"categories":["expression_statement"],"range":[0,2]}],"categories":["program"],"range":[0,2]}],"hasChanges":false,"range":[0,2],"number":1}],[{"terms":[{"children":[{"children":[{"children":{"\"b\"":{"children":[{"children":[{"categories":["StringLiteral"],"range":[4,5]},{"categories":["StringLiteral"],"range":[5,6]},{"categories":["StringLiteral"],"range":[6,7]}],"categories":["StringLiteral"],"range":[4,7]},{"patch":"replace","categories":["number"],"range":[9,10]}],"categories":["Pair"],"range":[4,10]}},"categories":["DictionaryLiteral"],"range":[2,12]}],"categories":["expression_statement"],"range":[2,12]}],"categories":["program"],"range":[2,12]}],"hasChanges":true,"range":[2,12],"number":2},{"terms":[{"children":[{"children":[{"children":{"\"b\"":{"children":[{"children":[{"categories":["StringLiteral"],"range":[4,5]},{"categories":["StringLiteral"],"range":[5,6]},{"categories":["StringLiteral"],"range":[6,7]}],"categories":["StringLiteral"],"range":[4,7]},{"patch":"replace","categories":["number"],"range":[9,10]}],"categories":["Pair"],"range":[4,10]}},"categories":["DictionaryLiteral"],"range":[2,12]}],"categories":["expression_statement"],"range":[2,12]}],"categories":["program"],"range":[2,12]}],"hasChanges":true,"range":[2,12],"number":2}],[{"terms":[{"children":[{"children":[{"children":{"\"a\"":{"children":[{"children":[{"categories":["StringLiteral"],"range":[14,15]},{"categories":["StringLiteral"],"range":[15,16]},{"categories":["StringLiteral"],"range":[16,17]}],"categories":["StringLiteral"],"range":[14,17]},{"categories":["number"],"range":[19,20]}],"categories":["Pair"],"range":[14,20]}},"categories":["DictionaryLiteral"],"range":[12,21]}],"categories":["expression_statement"],"range":[12,21]}],"categories":["program"],"range":[12,21]}],"hasChanges":false,"range":[12,21],"number":3},{"terms":[{"children":[{"children":[{"children":{"\"a\"":{"children":[{"children":[{"categories":["StringLiteral"],"range":[14,15]},{"categories":["StringLiteral"],"range":[15,16]},{"categories":["StringLiteral"],"range":[16,17]}],"categories":["StringLiteral"],"range":[14,17]},{"categories":["number"],"range":[19,20]}],"categories":["Pair"],"range":[14,20]}},"categories":["DictionaryLiteral"],"range":[12,21]}],"categories":["expression_statement"],"range":[12,21]}],"categories":["program"],"range":[12,21]}],"hasChanges":false,"range":[12,21],"number":3}],[{"terms":[{"children":[{"children":[{"children":{},"categories":["DictionaryLiteral"],"range":[21,22]}],"categories":["expression_statement"],"range":[21,23]}],"categories":["program"],"range":[21,23]}],"hasChanges":false,"range":[21,23],"number":4},{"terms":[{"children":[{"children":[{"children":{},"categories":["DictionaryLiteral"],"range":[21,22]}],"categories":["expression_statement"],"range":[21,23]}],"categories":["program"],"range":[21,23]}],"hasChanges":false,"range":[21,23],"number":4}],[{"terms":[{"children":[{"children":[],"categories":["expression_statement"],"range":[23,23]}],"categories":["program"],"range":[23,23]}],"hasChanges":false,"range":[23,23],"number":5},{"terms":[{"children":[{"children":[],"categories":["expression_statement"],"range":[23,23]}],"categories":["program"],"range":[23,23]}],"hasChanges":false,"range":[23,23],"number":5}]],"paths":["test/diffs/dictionary.A.js","test/diffs/dictionary.B.js"],"oids":["",""]}
\ No newline at end of file