diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,16 @@
 # Revision history for futhark-server
 
+## 1.3.0.0 -- 2026-03-05
+
+* `Futhark.Server.Values.getValue` now detects attempts to retrieve (some)
+  non-opaque values instead of silently producing something invalid.
+
+* `cmdSetTuningParam` now has a more precise type.
+
+* Server-related exceptions are now reported with the `ServerException` type.
+
+* `cmdFields` now produces structured information.
+
 ## 1.2.4.0 -- 2026-02-19
 
 * Report exit code when server terminates with nonzero exit code.
diff --git a/futhark-server.cabal b/futhark-server.cabal
--- a/futhark-server.cabal
+++ b/futhark-server.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.4
 name:               futhark-server
-version:            1.2.4.0
+version:            1.3.0.0
 synopsis: Client implementation of the Futhark server protocol.
 
 description: Provides an easy way to interact with a running Futhark
diff --git a/src/Futhark/Server.hs b/src/Futhark/Server.hs
--- a/src/Futhark/Server.hs
+++ b/src/Futhark/Server.hs
@@ -10,26 +10,32 @@
 -- functions for loading data into a server.
 --
 -- Error messages produced by the server will be returned as a
--- 'CmdFailure'.  However, certain errors (such as if the server
+-- t'CmdFailure'.  However, certain errors (such as if the server
 -- process terminates unexpectedly, or temporary files cannot be
 -- created) will result in an IO exception.
 --
 -- Many of the functions here are documented only as the server
 -- protocol command they correspond to.  See the protocol
 -- documentation for details.
+--
+-- Type aliases are added for readability, but many of the commands simply
+-- accept and produce 'T.Text's.
 module Futhark.Server
   ( -- * Server creation
     Server,
     ServerCfg (..),
     newServerCfg,
     withServer,
+    ServerException (..),
 
     -- * Commands
     Cmd,
     CmdFailure (..),
+    Field (..),
     VarName,
     TypeName,
     EntryName,
+    TuningParamName,
     InputType (..),
     OutputType (..),
 
@@ -89,9 +95,24 @@
 import System.IO.Temp (getCanonicalTemporaryDirectory)
 import qualified System.Process as P
 
+-- | An unexpected IO exception describing an error related to interacting with
+-- the server, such as failing to start it, or the server crashing.
+data ServerException
+  = -- | Human-readable error message.
+    ServerException T.Text
+  deriving (Show)
+
+instance Exception ServerException
+
 -- | The name of a command.
 type Cmd = Text
 
+-- | A record field
+data Field = Field
+  { fieldName :: Text,
+    fieldType :: TypeName
+  }
+
 -- | A handle to a running server.
 data Server = Server
   { serverStdin :: Handle,
@@ -131,11 +152,10 @@
       cfgOnLine = \_ _ -> pure ()
     }
 
--- | Start up a server.  Make sure that 'stopServer' is eventually
--- called on the server.  If this does not happen, then temporary
--- files may be left on the file system.  You almost certainly wish to
--- use 'bracket' or similar to avoid this.  Calls 'error' if startup
--- fails.
+-- | Start up a server. Make sure that 'stopServer' is eventually called on the
+-- server. If this does not happen, then temporary files may be left on the file
+-- system. You almost certainly wish to use 'bracket' or similar to avoid this.
+-- Throws 'ServerException' if startup fails.
 startServer :: ServerCfg -> IO Server
 startServer (ServerCfg prog options debug on_line_f) = do
   tmpdir <- getCanonicalTemporaryDirectory
@@ -152,9 +172,11 @@
   code <- P.getProcessExitCode phandle
   case code of
     Just (ExitFailure e) ->
-      error $ "Cannot start " ++ prog ++ ": error " ++ show e
+      throw . ServerException $
+        "Cannot start " <> T.pack prog <> ": error " <> T.pack (show e)
     Just ExitSuccess ->
-      error $ "Cannot start " ++ prog ++ ": terminated immediately, but reported success."
+      throw . ServerException $
+        "Cannot start " <> T.pack prog <> ": terminated immediately, but reported success."
     Nothing -> do
       let server =
             Server
@@ -171,19 +193,19 @@
     onStartupError :: Server -> IOError -> IO a
     onStartupError s _ = do
       code <- P.waitForProcess $ serverProc s
-      stderr_s <- readFile $ serverErrLog s
+      stderr_s <- T.readFile $ serverErrLog s
       removeFile $ serverErrLog s
-      error $
+      throw . ServerException $
         "Command failed with "
-          ++ show code
-          ++ ":\n"
-          ++ unwords (prog : options)
-          ++ "\nStderr:\n"
-          ++ stderr_s
+          <> T.pack (show code)
+          <> ":\n"
+          <> T.pack (unwords (prog : options))
+          <> "\nStderr:\n"
+          <> stderr_s
 
--- | Shut down a server.  It may not be used again.  Calls 'error' if
--- the server process terminates with a failing exit code
--- (i.e. anything but 'ExitSuccess').
+-- | Shut down a server. It may not be used again. Throws 'ServerException' if
+-- the server process terminates with a failing exit code (i.e. anything but
+-- 'ExitSuccess').
 stopServer :: Server -> IO ()
 stopServer s = flip finally (removeFile (serverErrLog s)) $ do
   hClose $ serverStdin s
@@ -191,10 +213,10 @@
   case code of
     ExitSuccess -> pure ()
     ExitFailure x -> do
-      stderr_s <- readFile $ serverErrLog s
-      error $
+      stderr_s <- T.readFile $ serverErrLog s
+      throw . ServerException $
         "Server terminated with nonzero exit code "
-          <> show x
+          <> T.pack (show x)
           <> " and stderr:\n"
           <> stderr_s
 
@@ -205,7 +227,7 @@
 abortServer = P.terminateProcess . serverProc
 
 -- | Start a server, execute an action, then shut down the server.
--- The 'Server' may not be returned from the action.
+-- The t'Server' may not be returned from the action.
 withServer :: ServerCfg -> (Server -> IO a) -> IO a
 withServer cfg m = mask $ \restore -> do
   server <- startServer cfg
@@ -280,18 +302,18 @@
       let code_msg =
             case code of
               Just (ExitFailure x) ->
-                "\nServer process exited unexpectedly with exit code: " ++ show x
+                "\nServer process exited unexpectedly with exit code: " <> T.pack (show x)
               Just ExitSuccess -> mempty
               Nothing -> mempty
-      stderr_s <- readFile $ serverErrLog s
-      error $
+      stderr_s <- T.readFile $ serverErrLog s
+      throw . ServerException $
         "After sending command "
-          ++ show cmd
-          ++ " to server process:"
-          ++ show e
-          ++ code_msg
-          ++ "\nServer stderr:\n"
-          ++ stderr_s
+          <> cmd
+          <> " to server process:"
+          <> T.pack (show e)
+          <> code_msg
+          <> "\nServer stderr:\n"
+          <> stderr_s
 
 -- | The name of a server-side variable.
 type VarName = Text
@@ -302,6 +324,9 @@
 -- | The name of an entry point.
 type EntryName = Text
 
+-- | The name of a tuning parameter.
+type TuningParamName = Text
+
 -- | The type of an input of an entry point.  If 'inputConsumed', then
 -- the value passed in a 'cmdCall' must not be used again (nor any of
 -- its aliases).
@@ -381,35 +406,41 @@
 cmdUnpauseProfiling s = helpCmd s "unpause_profiling" []
 
 -- | @set_tuning_param param value@
-cmdSetTuningParam :: Server -> Text -> Text -> IO (Either CmdFailure [Text])
-cmdSetTuningParam s param value = sendCommand s "set_tuning_param" [param, value]
+cmdSetTuningParam :: Server -> TuningParamName -> Int -> IO (Maybe CmdFailure)
+cmdSetTuningParam s param value = helpCmd s "set_tuning_param" [param, T.pack (show value)]
 
--- | @tuning_params@
-cmdTuningParams :: Server -> Text -> IO (Either CmdFailure [Text])
+-- | @tuning_params entry_point@
+cmdTuningParams :: Server -> EntryName -> IO (Either CmdFailure [TuningParamName])
 cmdTuningParams s entry = sendCommand s "tuning_params" [entry]
 
 -- | @tuning_param_class param@
-cmdTuningParamClass :: Server -> Text -> IO (Either CmdFailure Text)
+cmdTuningParamClass :: Server -> TuningParamName -> IO (Either CmdFailure Text)
 cmdTuningParamClass s param = fmap mconcat <$> sendCommand s "tuning_param_class" [param]
 
 -- | @types@
-cmdTypes :: Server -> IO (Either CmdFailure [Text])
+cmdTypes :: Server -> IO (Either CmdFailure [TypeName])
 cmdTypes s = sendCommand s "types" []
 
 -- | @entry_points@
-cmdEntryPoints :: Server -> IO (Either CmdFailure [Text])
+cmdEntryPoints :: Server -> IO (Either CmdFailure [EntryName])
 cmdEntryPoints s = sendCommand s "entry_points" []
 
 -- | @fields type@
-cmdFields :: Server -> Text -> IO (Either CmdFailure [Text])
-cmdFields s t = sendCommand s "fields" [t]
+cmdFields :: Server -> TypeName -> IO (Either CmdFailure [Field])
+cmdFields s t = fmap (zipWith parseField [1..]) <$> sendCommand s "fields" [t]
+  where
+    parseField :: Int -> Text -> Field
+    parseField l f =
+      case T.words f of
+        (fn : ft) -> Field fn $ T.unwords ft
+        _ -> error $ "Invalid field on line " ++ show l ++ " of `fields` output: \"" ++ T.unpack f ++ "\""
 
 -- | @new var0 type var1...@
-cmdNew :: Server -> Text -> Text -> [Text] -> IO (Maybe CmdFailure)
+cmdNew :: Server -> VarName -> TypeName -> [VarName] -> IO (Maybe CmdFailure)
 cmdNew s var0 t vars = helpCmd s "new" $ var0 : t : vars
 
 -- | @project to from field@
-cmdProject :: Server -> Text -> Text -> Text -> IO (Maybe CmdFailure)
+cmdProject :: Server -> VarName -> VarName -> Text -> IO (Maybe CmdFailure)
 cmdProject s to from field = helpCmd s "project" [to, from, field]
 
 -- | @shape v@
diff --git a/src/Futhark/Server/Values.hs b/src/Futhark/Server/Values.hs
--- a/src/Futhark/Server/Values.hs
+++ b/src/Futhark/Server/Values.hs
@@ -27,8 +27,10 @@
         case Bin.decodeOrFail bytes of
           Left (_, _, e) ->
             pure $ Left $ "Cannot load value from generated byte stream:\n" <> T.pack e
-          Right (_, _, val) ->
-            pure $ Right val
+          Right (remnant, _, val)
+            | LBS.null remnant -> pure $ Right val
+            | otherwise ->
+                pure $ Left "Cannot load opaque value."
 
 -- | Store a non-opaque value in the server.  A variable with the
 -- given name must not already exist (use 'cmdFree' to free it first