diff --git a/LICENSE b/LICENSE
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+++ b/LICENSE
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+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
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+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/exe/Main.hs b/exe/Main.hs
new file mode 100644
--- /dev/null
+++ b/exe/Main.hs
@@ -0,0 +1,123 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+-- based on the haskell-lsp example by Alan Zimmerman
+module Main (main) where
+
+import Control.Concurrent
+import Control.Concurrent.STM.TChan
+import qualified Control.Exception as E
+import Control.Monad
+import Control.Monad.Except (runExceptT)
+import Control.Monad.IO.Class
+import Control.Monad.STM
+import qualified Data.Cache as C
+import Data.Default
+import Data.Typeable (typeOf)
+import HsInspect.LSP.Context (BuildTool(..))
+import HsInspect.LSP.Impl
+import qualified Language.Haskell.LSP.Control as CTRL
+import qualified Language.Haskell.LSP.Core as Core
+import Language.Haskell.LSP.Messages
+import qualified Language.Haskell.LSP.Types as J
+import qualified Language.Haskell.LSP.Utility as U
+import System.Environment (getArgs)
+import System.Exit
+import qualified System.Log.Logger as L
+
+version :: String
+#ifdef CURRENT_PACKAGE_VERSION
+version = CURRENT_PACKAGE_VERSION
+#else
+version = "unknown"
+#endif
+
+help :: String
+help = "hsinspect-lsp [--help|version|stack]\n"
+
+-- TODO automated integration tests, e.g. using Emacs lsp-mode
+main :: IO ()
+main = do
+  args <- getArgs
+  when (elem "--help" args) $
+    (putStrLn help) >> exitSuccess
+  when (elem "--version" args) $
+    (putStrLn version) >> exitSuccess
+  let tool = if (elem "--stack" args) then Stack else Cabal
+  res <- run tool
+  case res of
+    0 -> exitSuccess
+    c -> exitWith . ExitFailure $ c
+
+-- TODO replace haskell-lsp (which is huge!) with a minimal jsonrpc
+--      implementation that covers only the things we actually support. The
+--      advantage would be to speedup installation for the user.
+run :: BuildTool -> IO Int
+run tool = flip E.catches [E.Handler ioExcept, E.Handler someExcept] $ do
+  rin <- atomically newTChan
+  let
+    dp lf = do
+      liftIO $ U.logs "main.run:dp entered"
+      _rpid <- forkIO $ reactor tool lf rin
+      liftIO $ U.logs "main.run:dp tchan"
+      return Nothing
+
+    callbacks = Core.InitializeCallbacks
+      { Core.onInitialConfiguration = const $ Right ()
+      , Core.onConfigurationChange = const $ Right ()
+      , Core.onStartup = dp
+      }
+
+  flip E.finally L.removeAllHandlers $ do
+    Core.setupLogger Nothing [] L.DEBUG
+    CTRL.run callbacks (lspHandlers rin) lspOptions Nothing
+
+  where
+    lspOptions = def
+    ioExcept   (e :: E.IOException) = print e >> return 1
+    someExcept (e :: E.SomeException) = print e >> return 1
+
+reactor :: BuildTool -> Core.LspFuncs () -> TChan FromClientMessage -> IO ()
+reactor tool lf inp = do
+  U.logs "reactor:entered"
+  caches <- Caches <$> C.newCache Nothing <*> C.newCache Nothing
+  forever $ do
+    inval <- atomically $ readTChan inp
+    case inval of
+
+      (ReqSignatureHelp req@(J.RequestMessage _ _ _ params)) -> do
+        U.logs $ "reactor:SignatureHelp:" ++ show params
+        let J.TextDocumentPositionParams (J.TextDocumentIdentifier doc) (J.Position line col) _ = params
+            Just file = J.uriToFilePath doc
+        res <- runExceptT $ signatureHelpProvider caches tool file (line + 1, col + 1)
+        case res of
+          Left err -> do
+            U.logs $ "reactor:signatureHelpProvider:err:" ++ err
+            -- FIXME how to send an error to the client?
+          Right sigs -> do
+            let render s = J.SignatureInformation s Nothing Nothing
+                halp = J.SignatureHelp (J.List $ render <$> sigs) Nothing Nothing
+            Core.sendFunc lf . RspSignatureHelp $ Core.makeResponseMessage req halp
+
+      -- TODO completionProvider
+      -- TODO definitionProvider
+
+      -- TODO DidOpenTextDocument is a good opportunity to preemptively populate caches
+
+      -- TODO hygienic registration of supported commands
+
+      om -> do
+        U.logs $ "reactor:HandlerRequest:" ++ (show $ typeOf om)
+
+lspHandlers :: TChan FromClientMessage -> Core.Handlers
+lspHandlers rin =
+  let passHandler :: (a -> FromClientMessage) -> Core.Handler a
+      passHandler c notification = atomically $ writeTChan rin (c notification)
+  in def { Core.signatureHelpHandler = Just $ passHandler ReqSignatureHelp
+         , Core.completionHandler = Just $ passHandler ReqCompletion
+         , Core.definitionHandler = Just $ passHandler ReqDefinition
+         , Core.initializedHandler = Just $ passHandler NotInitialized
+         , Core.cancelNotificationHandler = Just $ passHandler NotCancelRequestFromClient
+         , Core.didOpenTextDocumentNotificationHandler = Just $ passHandler NotDidOpenTextDocument
+         }
diff --git a/hsinspect-lsp.cabal b/hsinspect-lsp.cabal
new file mode 100644
--- /dev/null
+++ b/hsinspect-lsp.cabal
@@ -0,0 +1,86 @@
+cabal-version: 2.2
+name:          hsinspect-lsp
+version:       0.0.1
+synopsis:      LSP interface over the hsinspect binary.
+license:       GPL-3.0-or-later
+license-file:  LICENSE
+author:        Tseen She
+maintainer:    Tseen She
+copyright:     2020 Tseen She
+tested-with:   GHC ^>=8.4.4 || ^>=8.6.5 || ^>=8.8.3
+category:      Building
+description:   Inspect @.hs@ files using the ghc api.
+
+source-repository head
+  type:     git
+  location: https://gitlab.com/tseenshe/hsinspect.git
+
+-- https://www.haskell.org/cabal/users-guide/cabal-projectindex.html
+
+flag ghcflags
+  description: Generate .ghc.flags files during compilation
+  manual:      True
+  default:     False
+
+common deps
+  build-depends:
+    , aeson         ^>=1.4.6.0
+    , base          >=4.11    && <5
+    , bytestring
+    , cache         ^>=0.1.3.0
+    , directory
+    , extra         ^>=1.7.1
+    , filepath
+    , ghc
+    , ghc-paths
+    , hslogger
+    , process
+    , text
+    , transformers
+
+  ghc-options:      -Wall -Werror=missing-home-modules -Werror=orphans
+  default-language: Haskell2010
+
+  if flag(ghcflags)
+    ghc-options:        -fplugin GhcFlags.Plugin
+    build-depends:      ghcflags
+    build-tool-depends: hsinspect:hsinspect -any
+
+executable hsinspect-lsp
+  import:         deps
+  hs-source-dirs: exe
+  main-is:        Main.hs
+  ghc-options:    -rtsopts -threaded -with-rtsopts=-N8
+  build-depends:
+    , data-default
+    , haskell-lsp           ^>=0.22.0.0
+    , hsinspect-lsp
+    , mtl
+    , stm
+    , unordered-containers
+
+library
+  import:          deps
+  hs-source-dirs:  library
+
+  -- cabal-fmt: expand library
+  exposed-modules:
+    HsInspect.LSP.Context
+    HsInspect.LSP.HsInspect
+    HsInspect.LSP.Impl
+    HsInspect.LSP.Util
+
+test-suite test
+  import:             deps
+  hs-source-dirs:     test
+  type:               exitcode-stdio-1.0
+  main-is:            Driver.hs
+
+  -- cabal-fmt: expand test -Driver
+  other-modules:      HsInspect.LSP.HsInspectSpec
+  build-depends:
+    , hsinspect-lsp
+    , hspec          ^>=2.7.1
+
+  build-tool-depends: hspec-discover:hspec-discover ^>=2.7.1
+  ghc-options:        -rtsopts -threaded -with-rtsopts=-N8
diff --git a/library/HsInspect/LSP/Context.hs b/library/HsInspect/LSP/Context.hs
new file mode 100644
--- /dev/null
+++ b/library/HsInspect/LSP/Context.hs
@@ -0,0 +1,74 @@
+{-# LANGUAGE RecordWildCards #-}
+
+-- Calls to the hsinspect binary must have some context, which typically must be
+-- discovered from the file that the user is currently visiting.
+--
+-- This module gathers the definition of the context and the logic to infer it,
+-- which assumes that .cabal (or package.yaml) and .ghc.flags files are present,
+-- and that the build tool is either cabal-install or stack.
+module HsInspect.LSP.Context where
+
+import Control.Monad.IO.Class (liftIO)
+import Control.Monad.IO.Class (MonadIO)
+import Control.Monad.Trans.Except (ExceptT(..))
+import Data.List (isSuffixOf)
+import Data.List.Extra (trim)
+import HsInspect.LSP.Util
+import System.FilePath
+
+data Context = Context
+  { hsinspect :: FilePath
+  , package_dir :: FilePath
+  , ghcflags :: [String]
+  , ghcpath :: String
+  }
+
+findContext :: MonadIO m => DiscoverContext m -> FilePath -> m Context
+findContext DiscoverContext{..} src = do
+  ghcflags' <- discoverGhcflags src
+  ghcpath' <- discoverGhcpath src
+  let readWords file = words <$> readFile' file
+      readFile' = liftIO . readFile
+  Context <$> discoverHsInspect src <*> discoverPackageDir src <*> readWords ghcflags' <*> readFile' ghcpath'
+
+data DiscoverContext m = DiscoverContext
+  { discoverHsInspect :: FilePath -> m FilePath
+  , discoverPackageDir :: FilePath -> m FilePath
+  , discoverGhcflags :: FilePath -> m FilePath
+  , discoverGhcpath :: FilePath -> m FilePath
+  }
+
+data BuildTool = Cabal | Stack
+
+mkDiscoverContext :: BuildTool -> DiscoverContext (ExceptT String IO)
+mkDiscoverContext tool = DiscoverContext {..}
+  where
+    discoverHsInspect :: FilePath -> ExceptT String IO FilePath
+    discoverHsInspect file = do
+      let dir = takeDirectory file
+      dir' <- discoverPackageDir dir
+      case tool of
+        Cabal -> do
+          _ <- shell "cabal" ["build", "-v0", ":pkg:hsinspect:exe:hsinspect"] (Just dir') Nothing []
+          trim <$> shell "cabal" ["exec", "-v0", "which", "--", "hsinspect"] (Just dir') Nothing []
+        Stack -> do
+          _ <- shell "stack" ["build", "--silent", "hsinspect"] (Just dir') Nothing []
+          trim <$> shell "stack" ["exec", "--silent", "which", "--", "hsinspect"] (Just dir') Nothing []
+
+    -- c.f. haskell-tng--compile-dominating-package
+    discoverPackageDir :: FilePath -> ExceptT String IO FilePath
+    discoverPackageDir file = do
+      let dir = takeDirectory file
+          isCabal = (".cabal" `isSuffixOf`)
+          isHpack = ("package.yaml" ==)
+      locateDominating (\f -> isCabal f || isHpack f) dir
+
+    discoverGhcflags :: FilePath -> ExceptT String IO FilePath
+    discoverGhcflags file = do
+      let dir = takeDirectory file
+      (</> ".ghc.flags") <$> locateDominating (".ghc.flags" ==) dir
+
+    discoverGhcpath :: FilePath -> ExceptT String IO FilePath
+    discoverGhcpath file = do
+      let dir = takeDirectory file
+      (</> ".ghc.path") <$> locateDominating (".ghc.path" ==) dir
diff --git a/library/HsInspect/LSP/HsInspect.hs b/library/HsInspect/LSP/HsInspect.hs
new file mode 100644
--- /dev/null
+++ b/library/HsInspect/LSP/HsInspect.hs
@@ -0,0 +1,105 @@
+{-# LANGUAGE DeriveAnyClass #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE DuplicateRecordFields #-}
+{-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RecordWildCards #-}
+
+-- Abstraction of the hsinspect binary.
+--
+-- We intentionally do not depend on the hsinspect library because by decoupling
+-- the user can install one shared hsinspect-lsp binary for all projects, with
+-- only ghcflags / hsinspect setup per project.
+module HsInspect.LSP.HsInspect where
+
+import Control.Monad.IO.Class (liftIO)
+import Control.Monad.Trans.Except (ExceptT(..))
+import Data.Aeson
+import qualified Data.ByteString.Char8 as C
+import Data.Char (toLower)
+import Data.Text (Text)
+import GHC.Generics
+import HsInspect.LSP.Context
+import HsInspect.LSP.Util
+import qualified System.Log.Logger as L
+
+data HsInspect m = HsInspect
+  { imports :: Context -> FilePath -> m [Import]
+  , index :: Context -> m [Package]
+  }
+
+mkHsInspect :: HsInspect (ExceptT String IO)
+mkHsInspect = HsInspect {..}
+  where
+    imports :: Context -> FilePath -> ExceptT String IO [Import]
+    imports ctx hs = call ctx ["imports", hs]
+    index :: Context -> ExceptT String IO [Package]
+    index ctx = call ctx ["index"]
+
+    call :: FromJSON a => Context -> [String] -> ExceptT String IO a
+    call Context{hsinspect, package_dir, ghcflags, ghcpath} args = do
+      liftIO $ L.debugM "haskell-lsp" $ "hsinspect-lsp:cwd:" <> package_dir
+      stdout <- shell hsinspect (args <> ["--json", "--"] <> ghcflags) (Just package_dir) (Just ghcpath) [("GHC_ENVIRONMENT", "-")]
+      ExceptT . pure . eitherDecodeStrict' $ C.pack stdout
+
+data Import = Import
+  { _local :: Maybe Text
+  , _qual :: Maybe Text
+  , _full :: Text
+  } deriving (Eq, Show, Generic)
+
+data Package = Package
+  { _srcid :: Maybe Text
+  , _inplace :: Maybe Text -- bad Bool encoding
+  , _modules :: Maybe [Module]
+  , _haddocks :: Maybe [FilePath]
+  } deriving (Eq, Show, Generic)
+
+data Module = Module
+  { _module :: Text
+  , _ids :: Maybe [Entry]
+  } deriving (Eq, Show, Generic)
+
+data Entry =
+    Id { _export :: Maybe Exported
+       , _name :: Text
+       , _type :: Text }
+  | Con { _export :: Maybe Exported
+        , _name :: Text
+        , _type :: Text }
+  | Pat { _export :: Maybe Exported
+        , _name :: Text
+        , _type :: Text }
+  | TyCon { _export :: Maybe Exported
+          , _type :: Text
+          , _flavour :: Text }
+  deriving (Eq, Show, Generic)
+
+data Exported = Exported
+  { _srcid :: (Maybe Text)
+  , _module :: Text
+  } deriving (Eq, Show, Generic)
+
+jsonConventions :: Options
+jsonConventions = defaultOptions
+  { fieldLabelModifier = dropWhile ('_' ==)
+  , constructorTagModifier = map toLower
+  , sumEncoding = TaggedObject "class" ""
+  , omitNothingFields = True
+  }
+
+-- TODO DerivingVia this boilerplate away
+instance FromJSON Import where
+  parseJSON = genericParseJSON jsonConventions
+
+instance FromJSON Package where
+  parseJSON = genericParseJSON jsonConventions
+
+instance FromJSON Module where
+  parseJSON = genericParseJSON jsonConventions
+
+instance FromJSON Entry where
+  parseJSON = genericParseJSON jsonConventions
+
+instance FromJSON Exported where
+  parseJSON = genericParseJSON jsonConventions
diff --git a/library/HsInspect/LSP/Impl.hs b/library/HsInspect/LSP/Impl.hs
new file mode 100644
--- /dev/null
+++ b/library/HsInspect/LSP/Impl.hs
@@ -0,0 +1,91 @@
+
+-- Features of https://microsoft.github.io/language-server-protocol/specification.html
+module HsInspect.LSP.Impl where
+
+import Control.Monad.Extra (fromMaybeM)
+import Control.Monad.IO.Class (liftIO)
+import Control.Monad.Trans.Except (ExceptT(..))
+import Control.Monad.Trans.Except (throwE)
+import Data.Cache (Cache)
+import qualified Data.Cache as C
+import qualified Data.List as L
+import Data.Maybe (mapMaybe)
+import Data.Text (Text)
+import qualified Data.Text as T
+import qualified FastString as GHC
+import qualified GHC as GHC
+import GHC.Paths (libdir)
+import HsInspect.LSP.Context
+import HsInspect.LSP.HsInspect
+import qualified Lexer as GHC
+import qualified SrcLoc as GHC
+import qualified StringBuffer as GHC
+
+-- TODO consider more advanced cache keys, e.g. Import could be cached on a
+--      checksum of the file's header plus a checksum of the .ghc.* files.
+data Caches = Caches
+  (Cache FilePath Context) -- ^ by the package_dir
+  (Cache FilePath [Import]) -- ^ by source filename
+
+cachedContext :: Caches -> BuildTool -> FilePath -> ExceptT String IO Context
+cachedContext (Caches cache _) tool file = do
+  let discover = mkDiscoverContext tool
+  key <- discoverPackageDir discover file
+  let work = do
+        ctx <- findContext discover file
+        liftIO $ C.insert cache key ctx
+        pure ctx
+  fromMaybeM work . liftIO $ C.lookup cache key
+
+cachedImports :: Caches -> Context -> FilePath -> ExceptT String IO [Import]
+cachedImports (Caches _ cache) ctx file =
+  C.fetchWithCache cache file $ imports mkHsInspect ctx
+
+-- FIXME return all hits, not just the first one
+-- TODO docs / parameter info
+signatureHelpProvider :: Caches -> BuildTool -> FilePath -> (Int, Int) -> ExceptT String IO [Text]
+signatureHelpProvider caches tool file position = do
+  ctx <- cachedContext caches tool file
+  symbols <- cachedImports caches ctx file
+  sym <- symbolAtPoint file position
+
+  -- TODO include type information by consulting the index
+
+  let
+    matcher imp =
+      if _local imp == Just sym || _qual imp == Just sym || _full imp == sym
+      then Just $ _full imp
+      else Nothing
+
+  pure $ mapMaybe matcher symbols
+
+-- c.f. haskell-tng--hsinspect-symbol-at-point
+--
+-- TODO consider replacing this (inefficient) ghc api usage with a regexp or
+-- calling the specific lexer functions directly for the symbols we support.
+symbolAtPoint :: FilePath -> (Int, Int) -> ExceptT String IO Text
+symbolAtPoint file (line, col) = do
+  buf' <- liftIO $ GHC.hGetStringBuffer file
+  -- TODO for performance, and language extension reliability, find out how to
+  --      start the lexer on the correct line, to avoid lexing stuff we don't
+  --      care about.
+  buf <- maybe (throwE "line doesn't exist") pure $ GHC.atLine 1 buf'
+  let file' = GHC.mkFastString file
+      startLoc = GHC.mkRealSrcLoc file' 1 1
+      -- add 1 to the column because GHC.containsSpan doesn't seem to like it
+      -- when the point is on the very first character of the span and if we
+      -- must pick between the first or last char, we prefer the first.
+      point = GHC.realSrcLocSpan $ GHC.mkRealSrcLoc file' line (col + 1)
+  -- TODO construct the real dflags from the Context (remove libdir dependency)
+  dflags <- liftIO . GHC.runGhc (Just libdir) $ GHC.getSessionDynFlags
+  -- lexTokenStream :: StringBuffer -> RealSrcLoc -> DynFlags -> ParseResult [Located Token]
+  case GHC.lexTokenStream buf startLoc dflags of
+    GHC.POk _ ts  ->
+      let containsPoint :: GHC.SrcSpan -> Bool
+          containsPoint (GHC.UnhelpfulSpan _) = False
+          containsPoint (GHC.RealSrcSpan s) = GHC.containsSpan s point
+       in maybe (throwE "could not find a token") (pure . T.pack . snd) .
+            L.find (containsPoint . GHC.getLoc . fst) $
+            GHC.addSourceToTokens startLoc buf ts
+
+    _ -> throwE "lexer error" -- TODO getErrorMessages
diff --git a/library/HsInspect/LSP/Util.hs b/library/HsInspect/LSP/Util.hs
new file mode 100644
--- /dev/null
+++ b/library/HsInspect/LSP/Util.hs
@@ -0,0 +1,39 @@
+
+module HsInspect.LSP.Util where
+
+import Control.Monad.IO.Class (liftIO)
+import Control.Monad.Trans.Class (lift)
+import Control.Monad.Trans.Except (ExceptT(..))
+import Data.List (intercalate)
+import System.Directory (listDirectory)
+import System.Environment (getEnvironment)
+import System.Exit (ExitCode(..))
+import System.FilePath
+import qualified System.Log.Logger as L
+import qualified System.Process as P
+
+-- the first parent directory where a file or directory name matches the predicate
+locateDominating :: (String -> Bool) -> FilePath -> ExceptT String IO FilePath
+locateDominating p dir = do
+  files <- lift $ listDirectory dir
+  let parent = takeDirectory dir
+  if any p $ takeFileName <$> files
+  then pure dir
+  else if parent == dir
+       then ExceptT . pure . Left $ "locateDominating"
+       else locateDominating p parent
+
+shell :: String -> [String] -> Maybe FilePath -> Maybe String -> [(String, String)] -> ExceptT String IO String
+shell command args cwd path env_extra = ExceptT $ do
+  env <- getEnvironment
+  let env' = maybe env (\p -> ("PATH", p) : env) path
+      process = (P.proc command args) { P.env = Just (env_extra <> env')
+                                      , P.cwd = cwd }
+  liftIO $ L.debugM "haskell-lsp" $ "hsinspect-lsp:shell:" <> command <> " " <> intercalate " " args
+  (code, stdout, stderr) <- P.readCreateProcessWithExitCode process ""
+  case code of
+    ExitFailure i -> pure . Left $
+      concat [ "exit code: ", show i
+             , "\n stdout: ", stdout
+             , "\n stderr: ", stderr ]
+    ExitSuccess -> pure $ Right stdout
diff --git a/test/Driver.hs b/test/Driver.hs
new file mode 100644
--- /dev/null
+++ b/test/Driver.hs
@@ -0,0 +1,1 @@
+{-# OPTIONS_GHC -F -pgmF hspec-discover #-}
diff --git a/test/HsInspect/LSP/HsInspectSpec.hs b/test/HsInspect/LSP/HsInspectSpec.hs
new file mode 100644
--- /dev/null
+++ b/test/HsInspect/LSP/HsInspectSpec.hs
@@ -0,0 +1,27 @@
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE ViewPatterns #-}
+
+module HsInspect.LSP.HsInspectSpec where
+
+import Control.Exception (throwIO)
+import Data.Aeson
+import HsInspect.LSP.HsInspect
+import Test.Hspec
+
+spec :: Spec
+spec = do
+  let dir = "../tests/medley/library/"
+      parse :: HasCallStack => FromJSON a => FilePath -> IO a
+      parse p = do
+        res <- eitherDecodeFileStrict' (dir <> p)
+        case res of
+          Left reason -> throwIO $ userError reason
+          Right a -> pure a
+
+  it "should parse 'imports' results" $ do
+    decoded :: [Import] <- parse "Medley/Wibble.hs.ghc-8.8.3.imports.json"
+    decoded `shouldSatisfy` (not . null)
+
+  it "should parse 'index' results" $ do
+    decoded :: [Package] <- parse "ghc-8.8.3.index.json"
+    decoded `shouldSatisfy` (not . null)